Classification of Stars

Classification of Stars: 1.) Spectral Classification There are seven broad classifications and each is then subdivided into 10 sub-classes. The classes are: O, B, A, F, G, K, and M. A phrase to remember them would be: “Oh be a fine girl and kiss me.” Classification Color Temperature (K) Example O Blue-Violet 40,000-20,000 Mintaka B Blue 20,000-10,000 Spica Rigel A Green-White 10,000-7,000 Vega Sirius F Yellow-White 7,000-6,000 Canapo G Yellow 6,000 Sun K Yellow-Orange 4,000 Areturus Aldebaran M Red 3,000 Betelgeuse Barnard’s A star’s color is dependent upon its surface temperature. The hotter the temperature, the closer to blue the color becomes. The overall temperature is a function of surface area. Therefore, if the star expands in size its temperature per unit of surface area will decrease resulting in a change in color.

Hertzsprung - Russell Diagram The Hertzsprung – Russell (H-R) Diagram is a basic scatter plot diagram that plots a star’s color (temperature) versus its luminosity (absolute magnitude). There are various forms of the H-R diagram, but the common version has the vertical axis representing the star’s luminosity while the horizontal axis represents temperature in Kelvin. Luminosity is defined as the total energy radiated by a star each second, at all wavelengths. The units could be watts, similar to light bulbs, or more commonly, a ratio to our Sun is used. The absolute magnitude of the star is also used in some H-R Diagrams. The horizontal axis shows the temperature in Kelvin although one could also use spectral classification (O, B, A, F, G, K, and M), or both. Upon plotting the data of temperature and luminosity of nearby stars one sees a pattern starting to emerge. The stars form a band. This band is called the main sequence. The majority of stars, including our sun, fall into the main sequence band. However, there are stars that are outside the main sequence. One sees a group that is very bright, but yet cool. These stars are red giants and super giants. The other group of interest has a high temperature and is relatively dim. These stars are called white dwarfs.

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When the masses of stars are plotted versus their luminosity, on yet another form of an H-R diagram an interesting pattern is shown. The more mass a star has, the more luminous the star.

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Source: http://[email protected]/public/tutorial/HR.html Questions: 1.) How do we determine the distance to the stars? 2.) Why are stars of different masses and sizes? 3.) How do we explain those outliners from the main sequence?

Stars: Brightness

When we view the stars at night some appear brighter than others. Astronomers, since Hipparchus in 120 B.C. have referred to this system of comparison as apparent magnitude. The apparent magnitude scale uses the stars themselves and the brightest stars are said to one of first magnitude, the next brightest second magnitude. This classification proceeds until the faintest of stars at registered as sixth magnitude. Summary: The smaller the apparent magnitude, the brighter the star. In 1854 the apparent magnitude system was made exact and it is now agreed that a magnitude one star is exactly 100 times as bright as a magnitude 6 star. As there are 5 magnitudes between 1 and 6 and the total difference is 10^2, each whole number value on the magnitude scale differs from the next by a factor of 10^2/5, which is equal to 2.512. To put it another way, a first magnitude star is 2.512 times brighter than a magnitude two star. A first magnitude star is (2.512 x 2.512) times brighter than a third magnitude star and so on. Modern stellar magnitudes have been given values with two decimal places. For example: Deneb 1.25 Arcturus 0.00

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Sirius, the brightest star has a magnitude of -1.46. Remember, the smaller the magnitude number, the brighter the star appears, even if the numbers have to become negative. Polaris, the northern Pole Star has a magnitude of 2.00. Brightness is not kept to the stars; Astronomers also use the magnitude scale relative to the planets. Planet Apparent Magnitude Uranus 5.7 Venus -4.4 Jupiter -2.6 Sun -2.7 Pluto 14 There is a formula that relates the brightness of objects with their magnitudes. b1 / b2 = 10 ^ (2/5) (m1-m2) Where: b1 = brightness of star 1 b2 = brightness of star 2 m1 = magnitude of star 1 m2 = magnitude of star 2

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Stellar Brightness The Brightest Stars, as Seen from the Earth Adapted from Norton's 2000.0, 18th edition (copyright 1989, Longman Group UK) with additional comments taken from Bill Baity's Sky Pages

Common Name

Scientific Name

Distance (light years)

Apparent Magnitude

Absolute Magnitude

Spectral Type

Sun - -26.72 4.8 G2V Sirius Alpha CMa 8.6 -1.46 1.4 A1Vm Canopus Alpha Car 74 -0.72 -2.5 A9II Rigil Kentaurus Alpha Cen

4.3 -0.27 4.4 G2V + K1V

Arcturus Alpha Boo 34 -0.04 0.2 K1.5IIIp Vega Alpha Lyr 25 0.03 0.6 A0Va

Capella Alpha Aur 41 0.08 0.4 G6III + G2III

Rigel Beta Ori ~1400 0.12 -8.1 B81ae Procyon Alpha CMi 11.4 0.38 2.6 F5IV-V Achernar Alpha Eri 69 0.46 -1.3 B3Vnp Betelgeuse Alpha Ori ~1400 0.50 (var.) -7.2 M2Iab Hadar Beta Cen 320 0.61 (var.) -4.4 B1III

Acrux Alpha Cru 510 0.76 -4.6 B0.5Iv + B1Vn

Altair Alpha Aql 16 0.77 2.3 A7Vn Aldebaran Alpha Tau 60 0.85 (var.) -0.3 K5III Antares Alpha Sco ~520 0.96 (var.) -5.2 M1.5Iab Spica Alpha Vir 220 0.98 (var.) -3.2 B1V Pollux Beta Gem 40 1.14 0.7 K0IIIb Fomalhaut Alpha PsA 22 1.16 2.0 A3Va Becrux Beta Cru 460 1.25 (var.) -4.7 B0.5III Deneb Alpha Cyg 1500 1.25 -7.2 A2Ia Regulus Alpha Leo 69 1.35 -0.3 B7Vn

Adhara Epsilon CMa

570 1.50 -4.8 B2II

Castor Alpha Gem 49 1.57 0.5 A1V + A2V

Gacrux Gamma Cru 120 1.63 (var.) -1.2 M3.5III Shaula Lambda Sco 330 1.63 (var.) -3.5 B1.5IV

Source: http://www.astro.wisc.edu/~donlan/constellations/extra/brightness.htm Magnitudes

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The magnitude scale was invented by an ancient Greek astronomer named Hipparchus in about 150 B.C. He ranked the stars he could see in terms of their brightness, with 1 representing the brightest down to 6 representing the faintest. Modern astronomy has extended this system to stars brighter than Hipparchus' 1st magnitude stars and ones much, much fainter than 6.

As it turns out, the eye senses brightness logarithmically, so each increase in 5 magnitudes corresponds to a decrease in brightness by a factor 100. The absolute magnitude is the magnitude the stars would have if viewed from a distance of 10 parsecs or some 32.6 light years. Obviously, Deneb is intrinsically very bright to make this list from its greater distance. Rigel, of nearly the same absolute magnitude, but closer, stands even higher in the list. Note that most of these distances are really nearby, on a cosmic scale, and that they are generally uncertain by at least 20%. All stars are variable to some extent; those which are visibly variable are marked with a "v".

What are apparent and absolute magnitudes? Apparent is how bright the appear to us in the sky. The scale is somewhat arbitrary, as explained above, but a magnitude difference of 5 has been set to exactly a factor of 100 in intensity. Absolute magnitudes are how bright a star would appear from some standard distance, arbitrarily set as 10 parsecs or about 32.6 light years. Stars can be as bright as absolute magnitude -8 and as faint as absolute magnitude +16 or fainter. There are thus (a very few) stars more than 100 times brighter than Sirius, while hardly any are known fainter than Wolf 356.

Questions: 1.) How much brighter does Arcturus appear than Denab? 2.) How much brighter does Sirius appear than Uranus? 3.) Compare: Venus and Sirius Jupiter and Pluto Sirius and Polaris Polaris and Arcturus Alpha Centauri 1.4 and Barnard’s Star 9.5

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Distance to the Stars

It is time to use some of the geometry and trigonometry that you were taught. The distance to the nearer stars is determined by a method called trigonometric parallax. Let’s review a bit. Remember triangles? Take the one shown below for example.

We have an angle P, aside A and another side called D. All three of these are related by the trigonometric function called tangent. Tangent is defined in a right triangle as the ratio of the length of A the side opposite an angle to the length of the side adjacent to the angle. You may remember the formula: opposite over adjacent. In our above example the tangent of angle P equal A divided by D. Tangent of P = A / D By algebra, we can rearrange this formula to become: D = A / Tangent of P Getting back to the stars and using our trigonometry. The earth rotates around the sun in one year, so at six month intervals the Earth is to be found on opposite sides of the Sun.

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So this is how parallax works. In January we measure Star 1 relative to background stars. Six months later, in our case July, we photograph Star 1 again against the background stars. The change in position, measured as an angle is called 2P. If one were to draw a line between the Earth in January and the Earth in July a triangle would be formed. Further, if one draws a line from the sun to the Earth in January and then a line that dissects the angle 2P into halves, we would have the following:

Just like our original triangle. We know the distance from the Earth to the Sun as 149 million km. So the distance to a star can be calculated as:

d = 149,000,000 / Tangent of P

Where P is half the angle of parallax. Example: Alpha Centauri has an angle of parallax of 0.76 arc seconds. (0.76”) To find the distance:

d = 149,000,000 / Tan(0.76/60/60)º The question arises what is this (0.76/60/60)º thing?

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Let’s get back to the distance of stars a minute, because at this point, we need to understand……. Angles in the Sky: The Earth revolves once on its axis every 24 hours. This spin is in a circle. By definition, a circle is 360 degrees (360º). Further, it takes 24 hours to make the one rotation. If we divided the 360º by 24 hours, we can determine that each how of rotation covers 15 degrees of the total circle traveled.

360 degrees / 24 hours = 15 degrees/ hour

The distance, therefore, that the Sun appears to travel in one hour in the sky is 15 degrees. The diameter of the sun or moon is about a half a degree of distance in the sky. As we are traveling in the circular plane we refer to the distances as degrees of arc. A degree is made up of 60 minutes of arc (º) and a minute of arc is made up of 60 seconds of arc (“). A second (“), by definition is 1/(60x60) of a degree. This is similar to time where 1 second is 1/ (60x60) of an hour. A quarter seen from 10 km will be about 1” (1 second) of arc. Back to our discussion of parallaxes. As Alpha Centauri has an angle of parallax of 0.76 arc seconds and we need the angle in degrees, we divide 0.76 by (60x60), resulting in:

d = 149,000,000 / Tan (0.76/60/60) OR

4.04 x 10¹³ km This is a large number and not easily handled, so astronomers have come up with other measurements for distance. Presenting…….. The Astronomical Unit The astronomical unit is the average distance between the Earth and the Sun. Another measurement is… The Light Year, which is the distance light, going 300,000 km per second, travels in one year. This is 9,460,800 million km. Getting back to our formula of: d = A / Tan P /60 /60 Can be written to: Distance = [1AU x 180 x (360/π)] / 0.76 Where: au = astronomical unit = 1.4959 x 10^8 km d = distance to the star

d = (180 x 1466.49) AU / 0.76 d = 206,265 AU / 0.76 d = 271,401 AU

In other words, Alpha Centauri is 271,538 further away than the Sun. Using light years, 206,265 = 3.26 light years

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We can further substitute our equation: d = 3.26 LY /0.76 d = 4.30 LY We can now introduce a new unit of measure used by astronomers – the parsec. The parsec is defined as: 1.) 3.26 Light Years 2.) 206,264 AU 3.) If the parallax is 1”, then the distance can be determined mathematically as: d = AU x 180 x (3600 / π) = 206,264 AU = 3.26 LY = 1 parsec Summary: When the angle of parallax is expressed in seconds, the distance in parsecs will be equal to 1 divided by the parallax angle. d(parsec) = 1 / P (in arc seconds) Questions: Given the following parallax in arc seconds determine the distance in both parsec (pc) and light years (LY). Barnard’s Star 0.545” Wolf 359 0.425” Lalande 21185 0.398” Sirius 0.375”

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Absolute Magnitude When one observes stars from the Earth, the brightness of the stars does not take into account the distance of observation. If astronomers desire to compare the luminosity of stars the concept of Absolute Magnitude must be introduced. The concept of absolute magnitude is rather simple. Astronomers assume that the stars all occupy spaces on the same plane, equidistant from the observer. The agreed distance is 10 parsecs, or about 32 light years. The idea is to have all of the stars the same distance to see and compare the luminosities. The brightness of an object decreases with distance. It decreases by a function called the inverse square law. If the distance is doubled, the brightness decreases by a factor of four. The formula that relates absolute magnitude with apparent magnitude and distance is:

M = m + 5 – 5 log d Where: M = absolute magnitude m = apparent magnitude d = distance Interesting are the results of seeing the stars on equal footing, relative to distance. Star Apparent Magnitude Absolute Magnitude Sirius -1.46 1.41 Arcturus 0.00 -0.20 Aldebaran 0.85 -0.80 Deneb 1.25 -7.39 The Sun -27 4.71 Wolf 359 13.7 16.8

Luminosity: Luminosity is the amount of energy given out by a star. If we know the absolute magnitude of a star, the luminosity can be calculated.

Log 10 L = -0.4 M + 1.884 Where: L = Luminosity M = Absolute Magnitude Example: Deneb’s Luminosity Log 10 L = (-0.4 x -7.39) + 1.884 Log 10 L = 2.956 + 1.884 Log 10 L = 4.84 L = 10 ^4.84 = 69,183 Suns

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Questions: Determine the luminosity of the following stars. Sirius Arcturus Aldebaran The Sun Wolf 359

Mass-Luminosity Law For the majority of stars there is a simple relationship between mass and luminosity. L = M^3.5 Where: L = Luminosity (Suns) M = Mass (in Suns, or Solar Masses) Question: Graph the change in luminosity from a mass of 1 to a mass of 10.

Radius of a Star

Now, back to geometry. If we could measure the diameter of a star and assume the volume of sphere formula would be appropriate, much could be determined in the physical sense about a star. However, stars cannot be observed as a disk because of the distance. Outlined below are two methods that astronomers use to determine the radius of a star.

Stefan’s Law

Stefan’s Law relates the radius to the temperature of a star. Assuming that the amount of energy radiated by a square meter (1m²) of a star’s surface is dependent only on the temperature: R = sqrt. L / T² Where: R = Radius (Suns) L = Luminosity (Suns) T = Temperature (K) or (Suns) This implies that the higher the temperature, the more energy emitted. When two stars are the same temperature, but different in luminosity, then they must be of different size. Question: Determine the radii of the following stars. Assume the following: Diameter of the Sun = 1,390,000 km Star Temperature in Suns Sirius 2 Arcturus 0.66

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Interferometers

An interferometer is a device used to detect light emission from the opposite edges of a star. Based on the properties of waves, these almost parallel light waves interfere with each other. From this interference, and some very fine mathematics, the diameter of a star can be calculated.

Density

Density is defined as the mass of a substance per unit volume. For example, the density of water is 1 gram per cubic centimeter. 1gr/cm³. For stars, once we have determined the mass and radius, the density can be calculated. Density = M / R³ Where: M = Mass (Suns) R = Radius (Suns) Question: Given: Sirius A Mass = 2.28 Radius = 1.6 Sirius B Mass = 0.98 Radius = 0.022 Determine the densities, in Suns.

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Distances to the Stars

Distance (pc) = 1 / parallax (arc seconds) 1.) The parallax of Sirius is 0.38”. Find the distance in: a.) parsecs b.) light-years c.) kilometers 2.) Given the following parallax find the distance. Barnard’s Star 0.549” Atair 0.194” Thuban 0.176” Alpha Centauri 0.742” 3.) What constellations are the above stars located? 4.) What is the distance of an object given the following parallax? a.) 1 degree arc b.) 1 minute arc c.) 1 arc second 5.) What is a parsec? Compare it to an astronomical unit. 6.) How do astronomers determine a star’s luminosity? 7.) How do we determine stellar radii? 8.) Describe the characteristics of a red giant and a white dwarf. 9.) Compare absolute with apparent magnitude. 10.) How is stellar temperature determined? 11.) A star has a temperature twice that of the Sun and luminosity 64 times greater. What is the radius? 12.) D = 10pc x 10 A star has apparent magnitude of 10.0 and an absolute magnitude of 2.5. Find the distance.

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Life Cycles of Stars

Plants, animals, and even rocks have life cycles. Stars are no exception. Stars are born, live through a life, and have a death process. The final outcome of a star depends heavily upon its mass. Up to that point, however, the life cycles of all stars are similar. How and where do stars form? Why are there differences in mass and luminosities? These are some of the basic questions astronomers ask. Stars form in the matter among the stars called the interstellar medium. This interstellar medium is a mixture of gas and dust. The gas is composed of 90% hydrogen, 9% helium, and 1% heavier elements. The heavier elements include carbon, oxygen, silicon, magnesium, and iron. The composition of the dust is not well known but the size of a typical interstellar dust particle is about 1 x 10^-7 m. When the dust and gas collect in an area; the area has an appearance of being “cloudy.” These clouds of interstellar gas and dust are called Nebulae. Perhaps the reader is familiar with the Orion Nebula or the most recently imaged Horsehead Nebula. Star formation is most common to these areas of space because these vast areas of space contain what stars are made of. There are two basic types of Nebulae. First there is a reflection nebula which shines by reflecting the light of nearby stars. An emission nebula emits light as electrons recombine with protons to form hydrogen. The electrons were released by using the ultraviolet light emitted by nearby stars shinning through the hydrogen gas of space. There is also a nebula called planetary nebula which has resulted from the explosion of a star.

Formation of Average Stars (Our Sun is the Average Joe Six-pack)

Stage 1 A dense interstellar cloud starts to collapse. The clouds are vast, covering hundreds of parsecs. At this point, the temperature inside the cloud is about 10K with a density of particles of about 10^9 / m³. The cloud at this point forms small clumps perhaps forced together by interactions created by nearby stars. As the clumps condense, the cloud breaks apart resulting in many clumps of larger density than the original cloud. This process, to this point, will take a few million years. There is little evidence that stars form singularly. Usually many stars are born from these clumps. Stage 2 Let’s now concentrate on a Sun size forming cloud. At this point it will still be cool but in the neighborhood of 50 times larger than our solar system. The cloud fragment continues to contract and the radiation, at the center, struggles to escape the dense cloud and the center heats to 100K.

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Stage 3 Tens of thousands of years after the occurrence of stage 2, the temperature has increased to about 10,000K. The outer regions are still cool, but the size of the cloud fragment is about the size of the solar system. In the center one will find a dense opaque area called a protostar. The protostar’s radius is shrinking but its mass still continues to grow as gravity pulls material in from the surrounding area. When this stage is completed, a photosphere, or “surface” on the protostar can be distinguished. Inside the photosphere the energy generated cannot escape. Stage 4 The protostar shrinks, its density increases and the temperature rises, now at 1,000,000K. The size is about the size of Mercury’s orbit and atoms are being disassembled into subatomic particles. An accretion disk can be detected at this stage. The protostar is very luminous at this point due not to temperature, for the star has yet to “light.” The luminosity is due instead to the size of the star. Although not technically a star, the protostar can now be plotted on the Hertzsprung – Russell diagram. One would place it on the top quarter section. The protostar is relatively cool, but with a high luminosity. As the star evolves it follows a path that can be shown on the H – R diagram. This path of change is called the evolutionary track. The protostar is doing a balancing act at this point. Gravity between the atoms pulls inward while the temperature exerts an outward pressure. Still, the protostar continues to shrink and heat up. On the H – D diagram, the star moves toward higher temperature (to the left) and because of the decrease in size, downward to become less luminous. Stage 5 The protostar has now shrunk to a size equal to 10 times the Sun and has a surface temperature of 4,000K. The internal temperature has reached 5,000,000K and all of the atoms are now ionized. Although the protons are free, their electromagnetic repulsion keeps them apart. On the H – R diagram, the protostar is near the main sequence line. The process of contraction struggles. Contraction proceeds, but its rate is a function of the protostar’s ability to dissipate its heat into space. Stage 6 Grab the feet and slap. A star is born. Time has passed since conception of the star, about 10 million years. But the star has shrunk to a diameter of 2,000,000km and more importantly the internal temperature is now 10,000,000K. Nuclear burning can now start. Fusion. A star is born. The star is a bit larger than the sun and its luminosity is a bit less also. Stage 7 Over 25 million years, the star contracts. The core becomes denser, and its temperature rises to 15,000,000K. The surface is now 6,000K. Finally the star is on the main sequence line. As the gravity pulling equals the pressure pushing out, the star shines. But, death awaits this new born star.

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Stars / Chemistry / The Elements Fusion

The Bobby Seals of the Universe:

“Burn Baby Burn”

Stars generate their energy by means of fusion. This is a very important concept and we will detour from our star life cycle for a while to discuss fusion and its relationship to the formation of the elements. You see, all the elements have been made by activity of the stars. You are made of star stuff. Recall that hydrogen is made of 1 proton and 1 electron. Helium, the next element is made of 2 protons and 2 electrons. Lithium has three of each. Beryllium has 4 and so on. Carbon has 6 protons and 6 electrons. The protons can be found in the nucleus of an atom in close proximity. But how can protons, being of a similar positive charge, reside so closely? What could have forced these protons together? Fusion is the force and within stars is where it occurs. Fusion can be defined as the joining of objects. The electrical repulsion created by the positive charge of protons can be over come if the protons get very close. At 1 x 10^15 the “nuclear” or “strong” force can come into effect and the protons will stay together. To get fusion one must have high energies and a large density. At the core of a star, with temperatures of 7,000,000K, the atoms have been stripped of electrons and have enough energy to come close enough for fusion to occur. Below are the two major reactions of fusion that main sequence stars use. Our Sun “burns” hydrogen into helium and it is our first subject.

The Proton – Proton Reaction

At 15 million K our Sun has stripped the electrons from the protons in hydrogen atoms. Also, at that temperature when the protons collide they fuse creating a nucleus with the two protons. But one of the protons changes into a neutron through beta decay. This forms 2H which is call a deuteron. Beta decay also releases a positron and a neutrino. The positron, or positively charged electron, will collide with an electron and release 2 more gamma rays. Gamma rays are high energy photons. Neutrinos simply leave the Sun. Reaction #1 1H + 2H 2H + position (B) + neutrino (V) The next step can collide with another proton and form an isotope of helium, (3He) and releasing a gamma ray. Reaction #2 2H + 1H 3He + gamma ray (y) Lastly, when two 3He isotopes collide to form 4He, two protons are released. Reaction #3 3He + 3He 4He + 1H + 1H

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Please note that Reactions 1 and 2 must be done twice to feed one reaction #3. 3He and 4He are stable isotopes and the process in most main sequence stars ends at this step. Our Sun takes hydrogen, synthesizes helium and in the process, releases energy.

Fusion: The C – N – O Cycle

The hotter, and more massive stars use the carbon – oxygen cycle. The end result is still the conversion of hydrogen to helium. Remember hydrogen is still the most common element. Although hydrogen is the most common, some heavier elements do exist and if carbon, nitrogen, and oxygen are present at temperatures greater than 16 million K, the following sequence of reactions will occur. 1.) 12C + 1H 13N + gamma ray 2.) 13N 13C + (B) + neutrino 3.) 13C + 1H 14N + gamma ray 4.) 14N + 1H 15O + gamma ray 5.) 15O 15N + (B) + neutrino 6.) 15N + 1H 12C + 4He Carbon acts as the catalyst for this reaction. Appearing in both the first, and the last step, but remaining unchanged.

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NUCLEAR FUSION IN STARS

The basic energy producing process in the sun is the fusion of hydrogen nuclei into helium nuclei. This can take place in several reaction sequences, the most common of which is the Proton - Proton cycle, shown below:

Q1) Draw out the diagram and label each particle , using the key.

Q2) Write equations for the second and third reactions. The first has been done for you.

Q3) Why is this a 'cycle' ?

On the earth, 150 million km from the sun , each square metre receives energy at the rate of 1.4 kW.

Q4) Calculate the total energy radiated by the sun per second.What has been assumed here ?

Carefully examine the three stages of the cycle. If we ignore the contribution of the gamma rays and the antineutrinos ,then the energy evolved per cycle is given by

E = (Δm)c2 , where Δm is the net mass difference.

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Mass-Energy Equivalence .

Q5) Explain why Δm = 4Mp - (Mα + 2 Me).Show that this mass difference evaluates to about 24.7 MeV.(Note: Most data books gives masses for isotopes , not nuclei - ie the relevant numbers of electrons are included. Compare Eg 1H with proton mass)

Q6) Fom your answers to Q4 and Q5 show that the p-p cycle must occur approximately 1038 times a second

Q7) The mass of the sun is 2x1030kg. Assuming that initially all the mass of the sun was protons, how many does this correspond to ? If four are used up each time, show that the total possible energy release is about 1.2x1045 J

Q8) Using your answers to Q4 and Q7 show that the lifetime of the sun could be 3x1018seconds . How many years is this ? Comment.

(Shine on you crazy diamond!!)

Self sustaining fusion reactions can only occur under conditions of extreme temperature and density. The core of the sun is believed to be at a temperature of about 1.5 x 107 K which is sufficient for the p-p cycle to occur there.

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Q9) How does this temperature compare with the ' threshold ' temperatures for the elementary particles that calculated in the 'Big Bang ' exercise ? Comment.

CARBON CYCLE IN STARS

Hotter stars than the sun can sustain the Carbon cycle; this is pictured below:

Q10) There are six different nuclear reactions occurring in this cycle. Write full nuclear equations for them. One has been done for you .

Q11) Which species acts as a 'Catalyst' for the process? What is the net result of this cycle ? Calculate the energy output per cycle in MeV and comment.

Q12) When much of the hydrogen has been used up, the radiation pressure in the star will drop. Which force will now become important ? What effect will this have ?

A temperature of about 108K is needed for helium fusion to begin an example is

3 4He --> 12C

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Q13) Show that the energy evolved from this process is about 7.5 MeV

Other examples include 4 He +12C -> 16O and 2 12C --> 20Ne + 4He

Calculate the energy for these processes.

BINDING ENERGY CURVE

In heavier stars the temperature is higher. In stars of about 10 solar masses , the iron isotope 56Fe is reached. This is the heaviest nucleus that can be formed in the core of stars by nuclear fusion.

Q14) The binding energy per nucleon is found by dividing its total binding energy by the number of nucleons it contains.

Show that the binding energy of deuterium is 2.2MeV.(Assuming it is made from a hydrogen isotope plus a neutron) and that its binding energy per nucleon is thus 1.1MeV

Q15) Suggest what nucleus gives the sharp spike on the graph. What nucleus will yield the maximum on the graph ? What consequences does this have for nuclear fusion and element synthesis inside stars ?

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Q16) Show that for your chosen maximum element that the binding energy is 492.5 MeV and that the binding energy per nucleon is 8.8MeV. State clearly any assumptions you make. Repeat this calculation for a different element in the 'Fission' range and comment.

Q17) Try to find out how heavier nuclei are made. Encarta and Redshift 2 software are useful.

Q18) The isotope of Bismuth 209Bi contains the largest known binding energy. Calculate this value and show that its binding energy per nucleon is considerably less than 8.8MeV.

Q19) This bismuth isotope is thought to be the heaviest that can form in the cores of stars. Why ? Isotopes of masses up to 260 amu may form. Where ? and why ?

Q20) Try to find out what you can about Solar Neutrinos and their importance.

Source: http://www.egglescliffe.org.un/physics/particles/sun/sun.html

Questions: 1.) Why are high temperatures and densities required for fusion? 2.) Which process is used by our Sun? 3.) Describe the proton – proton reaction.

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Stars of Other Masses

It should be emphasized that stars evolve to the main sequence, not along the line. Reason would suggest that the more massive stars were born from more dense cloud fragments. This is true. Furthermore, if the clouds also contained heavier elements, they will find themselves captured by the forming stars. But not all stars ignite. Jupiter, our solar system’s massive planet is thought to be a failed star. Although it generates heat from within it became stabilized by heat and rotation before the central temperature became hot enough to start fusion. There are numerous objects similar to Jupiter in the universe. They are small, faint, and cooling. A brown dwarf is the collective term. They are failed stars.

Stellar Evolution

Stars spend tens of millions of years forming before joining the main sequence. Many will spend billions of years on the main sequence. What happens then? What determines the amount of time spent on the main sequence? These questions can be answered by the study of stellar evolution. A star, on the main sequence, uses the process of fusion to burn hydrogen into helium. This process is called core hydrogen burning. The amount of time spent burning is a function of two variables: the rate of burning and the amount of hydrogen. This implies that the larger, brighter, and hotter stars reach the point of fuel exhaustion earlier than smaller cooler stars. This assumption would indeed be true. As has been pointed out, a star is in hydrostatic equilibrium. The pressure generated by hydrogen fusion, which is an outward push and an inward pull of gravity become equivalent to one another. A star’s behavior as it ages can be understood with this basic concept held in mind. As stars on the main sequence age their core temperature rises and their radius expands. This occurs very slowly. The luminosity, as a function of the temperature and radius also increases. Eventually the hydrogen at the core is consumed, resulting in changes, both externally and internally. Relative to the H – R diagram, the star leaves the main sequence. The star’s days are numbered. The type of death that the star will experience will depend on the mass of the star itself. There are two basic outcomes of a star’s death with a dividing line between the two lying somewhere around a mass of 8 solar masses (low mass stars) the stars die a gentle death. With a mass of 8 or more (high mass stars) the end is extremely violent. Within each group, high mass or low mass stars, there are variations. These variations will be pointed out later on.

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Sun-like Stars

Our Sun was formed some 5 billion years ago. The surface area has remained constant but the luminosity has increased by about 30 percent. As our Sun runs out of hydrogen, the interior will change. Quantitatively speaking, the amount of hydrogen decreases while the amount of helium increases. Helium accumulates in two areas of the star, at the core and at the edge of the core. In time, the center becomes completely depleted of hydrogen. The fusion at the core stops at this point and the burning now occurs at a higher level in the core. The core now has a high amount of non-burning pure helium. Because the core, at the center, is no longer burning the outward pressure is slacked a bit. The inward pressure of gravity has not been relieved and something has to give; as the hydrogen is consumed, the inner core contracts. With depleation the contraction accelerates. If the helium-composed core could start fusion into heavier elements, the star can regain stability. The problem is, however, that hydrogen can undergo fusion at a temperature of 10^7K while helium requires a temperature of 10^8K for fusion. The shrinking core releases gravitational energy and drives the core temperature up. This causes the hydrogen to burn even faster. While the center of the core isn’t burning, the shell of the core is, and at a furious rate. This stage is referred to as the hydrogen-shell burning stage. So we have the core shrinking and the outer shell of the core producing more energy resulting in the star getting brighter. Pressure created by the enhanced hydrogen burning expands the outer layers of the star, while the core is shrinking and heating up. The star is becoming a red giant. From the main sequence to a red giant will take 100 million years. Back to the H – R diagram. The star has left the main sequence line and now inhabits the area in the upper right hand quarter, cooling slightly but also becoming more luminous. Our sun, at this point will be three times its normal size. Gone will be all of the terrestrial planets. The Sun will occupy what is called the red-giant branch of the H – R diagram. For a star the size of our Sun, the shrinking and expanding do not go on indefinitely. Next, in our chain of events, the helium begins to burn at the core, making carbon. Below is the reaction. 4He + 4He 8Be + energy 8Be + 4He 12C + energy This series of reactions is called the triple – alpha process. At the core, electrons from the atoms have been stripped and are now supporting the core from further contraction by a process called electron degeneracy. Imagine the electrons being compacted together but the electrons, themselves, are incompressible. For a few hours, the helium burns. This creates a “helium flash”. The heat generated restores the outward pressure created by a high temperature. The core expands and equilibrium between the inward pull of gravity and the outward push of gas pressure is reestablished. The core burns helium into carbon at temperatures well above 10^8K.

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On the H – R diagram, the helium flash expands and cools the core thus reducing the luminosity. The temperature does increase. On the diagram, the star moves downward and to the left. After a few tens of millions of years, the helium is consumed. When the helium is gone, fusion stops yet again. The core shrinks again causing the outer layers of the core, where the hydrogen to helium burning is still taking place, to increase their rates of burning. Imagine the following: The star now has a shrinking carbon core surrounded by a helium burning shell which is in turn, surrounded by a hydrogen burning shell. The outer parts of the star are starting to expand, similar to the first time it became a red giant. The star has become a red giant a second time. The star is a red Super giant. On the H – R diagram our red super giant now resides vertically upward from where it was located. Luminosity, but no temperatures have been increased. This is caused by the shrinking core which drives the outer core layers to higher temperatures. The core becomes too cool for fusion in our sun-size star. If the central temperature could become high enough however, further fusion into heavier elements could occur. A temperature of 600 million K would be required for elements heavier than carbon to be synthesized. With a solar mass of less than 8 this re-ignition does not occur. Total mass of the star creates the downward pressure of gravity and with low mass stars there simply isn’t enough mass pushing down to build up enough heat to reignite. There is enough heat and pressure for one last fusion at the edge of the carbon core and the helium burning shell. 12C + 4He 16O + energy Let’s summarize the state of our star. 1.) The inner carbon core no longer generates energy. 2.) The outer core shells continue to burn hydrogen and helium. 3.) The core is shrinking. 4.) The outer envelope of star continues to expand and cool. In time, an object that many are familiar with emerges: a planetary nebula. Seen with a core of carbon and cooling rings surrounding it, planetary nebulae are perhaps some of the more artful creations in the universe. The “ring” of the planetary nebula is really a three-dimensional shell of cooling gas surrounding the core. The shell continues to expand over time leaving the core to cool, alone. The core for our sun will be the size of the Earth and will shine from stored heat and will appear to be white. It is called a white dwarf, composed of carbon and oxygen usually. For stars larger than our sun, but yet smaller than 8 solar masses, an additional fusion process; 16C + 4He 20Ne + energy may have occurred before the planetary nebula stage resulting in a neon – oxygen white dwarf.

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The white dwarf does not contract as it cools but simply darkens to the characteristic blackness of carbon. Over time it becomes a black dwarf.

White Dwarfs and Novae

Nova means “new” in Latin. Early astronomers saw bright flashes of what they thought were new stars. In reality, a nova is a white dwarf undergoing an explosion on its surface which dramatically increases the luminosity for a few days. How does this happen? Many stars are but one of a pair. Called a binary system, they orbit each other, or around a fixed point. If one of the stars has become a white dwarf and is close enough to the still-burning star, then the dwarf may pull some of the hydrogen and helium from the star by means of gravity. As the gas accumulates on the white dwarf, it gets denser and hotter. When the temperature of the dwarf reaches 10^7 K the process of fusion stars, creating helium. This burning on the surface is hot and luminous, but brief. Recurrent novae repeat the process many times.

High Mass Stars

High mass stars evolve faster than low mass stars. Our sun will spend some 10 billion years in the main sequence. A 10-solar-mass O-type star will last only about 20 million years. Evolution of higher mass stars is the result of the high mass and stronger gravitational pull, which generates more heat. This increase in heating speeds up the nuclear reactions in the star. Similar to the low mass stars, the high mass stars leave the main sequence to join the red giant section of the H – R diagram. From there, the tracks of the low and high mass stars diverge. For stars at and above 8 solar masses, they can fuse carbon, oxygen and even high elements, as the core contracts and the temperature exceeds 600 million K. All the elements on the periodic table are synthesized until the element iron is made. Once the core begins to become iron, the process of fusion becomes difficult for iron is a very stable element. Fusion of 3helium releases energy to form carbon, because there is a net loss in the nucleus. To combine iron nuclei requires input. The center of the core no longer burns when iron is formed. Equilibrium, just like the lower mass stars is gone. Even though the core is several billion Kelvin, the gravitational pull of matter overcomes the outward gas pressure and the star implodes upon itself. At 10 billion K and with the energy of implosion, iron is split into lighter nuclei and those nuclei into lighter nuclei until only protons and neutrons exist. This process is called photodisintegration. With the iron broken down, the core is compressed to a great density. But as Newton would remind us, for every action there is an equal and opposite reaction. When the iron core is compressed to the maximum it rebounds, violently. A great energetic shock wave resonates from the center of the star blasting all of the outside

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layers containing heavier elements into space. A core-collapse supernova has just happened.

The Element Beyond Iron

If the largest of stars have the synthesis of elements stop at iron, how did the heavier elements form? They formed by the process of neutron capture. Deep in the core of a star neutrons are produced as by products of nuclear reactions. Because neutrons don’t have a charge, they are absorbed by the iron nucleus. At this point we simply have isotopes of iron, not a new element, but the new iron element undergoes radioactive decay and becomes a new element. The process could work as it is illustrated below: 56^Fe + n 57^Fe 57^Fe + n 58^Fe 58^Fe + n 59^Fe Iron-59 is know to be radioactively unstable and will decay to form Cobalt-59. Cobalt-59 captures a neutron and it decays to form Nickel-60, and so on. This process is slow and is called the s-process. The s-process can be justified in the explanation, by experimental evidence, for the creation of heavier elements is up to Bismuth-209. Beyond that element however, the explanation does not work for the isotopes formed at that point decay back to Bismuth-209 as quickly as they are formed. The r-process, or rapid process, explains the formation of the heavier elements such as Uranium-238. During the first minutes of a supernova blast, there are a great number of neutrons produced. These neutrons are jammed into the heavy and middle weight nuclei forming the heaviest of the elements.

Novae and Supernovae

Like a nova, a supernova is a star that suddenly increases in brightness and then dims. The exploding star is called the supernova’s progenitor. And although both nova and supernova give a brief brightness, the supernova has much more energetic events. Within the classification of supernovae, there are two subclasses: Type 1 supernovae and Type 2 supernovae. Type 1 supernovae is a hydrogen poor environment whereas a Type 2 supernovae environment has a hydrogen rich environment. A Type 2 supernovae is the same at a core-collapse supernova. This is when the star collapses into its iron core and then rebounds sending material into space. Type 1 supernova, the type with out hydrogen, are further subdivided into three classes: Type 1a: no hydrogen lines, no helium lines and strong silicon lines. Type 1b: no hydrogen lines, but strong helium lines. Type 1c: no hydrogen lines, no helium lines, and no silicon lines.

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Having dissected the types of supernovae, a bit of clarification is in order. Type 1b and 1c supernovae are massive stars which lost their outer layers before they collapsed. Type 1b and 1c are basically the same as type 2 supernovae. The only differences are the contents of the outer part of the star before the collapse. Type 1a supernovae involve a white dwarf in a binary system. As the main sequence star expands into a red giant, the white dwarf will accumulate material. The mass of the white dwarf increases. As the mass increases: 1.) The radius decreases. 2.) The temperature increases. At this new and higher density, the temperature of the white dwarf starts the fusion of carbon and oxygen to create iron. The result is a fusion explosion, emitting vast quantities of energy.

Chandrassekhar Limit The Chandrassekhar Limit is a limit which mandates that no white dwarf can be more massive than 1.4 solar masses, and a degenerate object (collapsed star) more massive must inevitably collapse into a neutron star.

Neutron Stars

It is doubted that Type 1 supernovae leave anything of the core after the explosion. Type 2 however, could leave part of the center. Models suggest that the only particle left in the core would be neutrons. This core remnant is called a neutron star, although all of its nuclear reactions have stopped. Neutron stars are very small and very massive. Only about 20km, in diameter they are composed solely of neutrons. Their density can reach 10^17kg/m³. This would imply an intense gravity. Neutron stars rotate rapidly and have very strong magnetic fields.

Pulsars

Objects that emit radiation in the form of rapid pulses with a characteristic pulse period and duration is a pulsar. Pulsars are still not completely understood. It is reasoned however, that the high-energy radiation emitted is due to a misalignment of a neutron star’s rotation axis with its magnetic field. This release of energy results in pulses of energy, or beams, sweeping through space, similar to the beams of light from a lighthouse. All pulsars are neutron stars, but not all neutron stars are pulsars. This is because the two ingredients for a pulsar, rapid rotation, and strong magnetic field, diminish over time. Furthermore, only if the neutron star is oriented in just the right way can we offer detection.

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Pulsars have been detected at many wavelengths. The list includes the radio, optical, x-ray, and gamma-ray wavelengths. The size limit for a neutron star is about 3 solar masses.

Black Holes

Can gravity compress matter further than a neutron star? Remember that a neutron star is a solid ball of neutrons. What are the limits of gravity? These questions are the cutting edge of theoretical astronomy. Apparently, we don’t completely comprehend that force on Newton’s apple. If enough material is left behind after a supernova, such that it exceeds 3 solar masses, then gravity crushes the remaining matter and the central core collapses forever. Theory indicates that any star mass above 25 solar masses has this fate awaiting. As the stellar core shrinks, the pull of gravity becomes so great, because of its density, that even light is unable to escape. This is known as a black hole.

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Star Life Cycle

1.) Where are new stars born? 2.) List the 3 main steps in the birth of a star. 3.) What is the “main sequence”? 4.) What is the source of energy for stars in the main sequence? 5.) Relate mass to the length of a star’s life. 6.) What event causes a star to become a red giant? 7.) Carbon and Oxygen are made where in the universe? 8.) What determines the way a star finally dies? 9.) What is a planetary nebula and how is it formed? 10.) What is a white dwarf star? 11.) For a star about the same mass as our Sun, describe the life cycle. 12.) Describe the life cycle for a star 25 times the size of our Sun.

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13.) Relative to stars, why is there more abundance of lighter elements than heavier elements? 14.) Compare the gravity of a pulsar to that of the Earth. Explain your answer. 15.) High mass stars start off with more fuel than a low mass star. Why don’t they live longer?

H – R Diagrams 1.) Using the given locate the stars on the H – R diagram. Star Magnitude Spectral Class Rigel -6.6 B Vega 0.6 A Sun 4.8 G Betelguese -5.0 M Barnard’s Star 13.2 M 2.) What determines a star’s location on the H – R diagram? Or, what determines a star’s luminosity and temperature?

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Optical Telescopes

Since Galileo, astronomers have been using optical telescopes to observe the cosmos. An instrument used to capture as many photons as possible from a given region in space and concentrate them into a focused beam for analysis. Optical telescopes fall into two basic categories: reflectors and refractors. Both have their advantages as well as disadvantages. Both share common characteristics and abilities.

Reflectors

A telescope is classified by the part of the telescope that gathers the light, or objective. For a reflecting telescope a curved, or concave, mirror is used. The curved nature of the mirror concentrates the beam of light. The mirror is called the primary mirror because telescopes often have more than one mirror, concentrating the beam of light on a single point called the focus. The distance between the primary mirror and the focus is called the focal length. Astronomers call the focal point the prime focus.

Refractors

Refracting telescopes use a lens to gather and focus the incoming light. Refraction is a term that refers to the bending of light as it travels from one medium to another. In our case, the two mediums are air and the glass of the lens. In refraction telescopes, the objective lens is convex. The first telescopes built were refractors. There are advantages and disadvantages to both types of telescopes. Refractor Telescopes Advantages: 1.) Rugged. Once constructed they seldom require realignment. 2.) Because the lens is held at the end of a sealed tube from the eyepiece, this telescope rarely needs to be cleaned. 3.) Because of the sealed tube, air currents and temperature changes that affect the focus are reduced. Disadvantages: 1.) Chromatic aberration. All refractor telescopes have this problem to some degree. Chromatic aberration is a condition that creates a rainbow of colors around the image. When light passes through a prism, a rainbow of color is created. The rainbow is a result of the longer wavelength light (red) being bent less than the shorter wavelength light (blue). This can ruin an image. There are two ways to control chromatic aberration. One can use a set of lenses or make the focal length of the telescope very long.

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2.) How well the light passes through the lens varies with the wavelength. Ultraviolet light does not pass through a lens at all. 3.) The thicker the lens, the less light that passes through. 4.) It is difficult and expensive to build a high quality lens. 5.) The objective lens can only be supported at the edges and large ones have a tendency to sag, creating distortions. Reflectors Advantages: 1.) Reflectors do not suffer from chromatic aberration. 2.) The primary mirror is at the end of the telescope so they can be made very large. 3.) Cheaper than refractors to make. 4.) Because light is reflecting off of the mirror, or objective, only one side has to be perfect. Disadvantages: 1.) It is easy to get the optics out of line. 2.) Because a reflector is open, it requires frequent cleaning. 3.) Often a secondary mirror is used and this secondary mirror can distort the image. Common to both types of telescopes is a defect call spherical aberration. This is a condition caused when not all of the light is focused at the same point. In mirrored telescopes it occurs when the mirror is not curved at the proper angle. The Hubble had this problem because of a curve defect the width of 1/50th of a human hair. In reflectors it occurs when the lens is not shaped correctly.

Types of Reflecting Telescopes

Although there are many types of reflecting telescopes there are two basic designs that are widely used. The Newtonian telescope intercepts the light from the primary mirror before it reaches the prime focus and deflects it to an eyepiece located on the side of the telescope. This type of telescope is named in honor of its inventor, Sir Isaac Newton. If an astronomer wants to work from behind the telescope and desires a reflector, the Cassegrain telescope design is his choice. After the light is reflected oof the prime mirror, it is intercepted by the secondary mirror which redirects the light back down through a small hole in the primary mirror to the eyepiece.

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Telescope Types

What are those numbers?

The f-ratio is the focal length divided by the diameter of the telescope. Magnification

is the focal length of the telescope divided by the focal length of the eyepiece.

Example:

To find the f-ratio of a telescope 10 " in diameter with a 45" focal length:

o Divide 45 " F.L. by10" D. to get an f-ratio of 4.5.

To compute magnification:

First, convert focal length to mm: 45" = 1146 mm; then:1146 mm focal length divided by 35 mm eyepiece equals 33 magnification.

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Source: http://www.seattleastro.org/paths.html Questions: Reflector and Refractor Telescopes 1.) What are the two basic types of telescopes? 2.) What are the advantages and disadvantages of both? 3.) Why are the large modern telescopes reflectors? 4.) Refractor telescopes sometimes produce rainbows around the image. Explain why this occurs. 5.) How will spherical aberration affect an image?

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Magnification

Irregardless of which type of telescope is being used, the principle of observing the image is the same. Light is focused and viewing is then done by looking at the image through a lens called an eyepiece. The eyepiece is similar to those used in microscopes. Eyepieces magnify the image. One can change the magnification of a telescope by simply changing the eyepieces. Eyepieces have different focal lengths and the rule of thumb is that the shorter the focal length the higher the magnification. The magnification of the image is not solely dependent upon the eyepiece, however, because the total magnification of the image is a function of both the eyepiece and the focal length of the telescope. To find the magnification power of any telescope one divides the focal length (f.l.) of the telescope by the focal length of the eyepiece. Magnification = Objective f.l. / Eyepiece f.l. OR Magnification = focal length of the objective / Focal length of the eyepiece Questions on Magnification: 1.) We have 3 telescopes that have the following focal lengths: 2000mm 800mm 450mm Calculate the magnification power of each, using the three eyepieces below: 8mm 12mm 26mm 2.) Using the formula for magnification power, explain why astronomers want a long focal length.

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Telescope Size

Astronomers like large telescopes for two reasons. First, the larger the aperture the mare light it can collect. Secondly, the larger aperture has a larger resolving power. Resolution, or resolving power, is nothing more than the ability to see details of the image. Larger telescopes have a larger collection area for light. Remember that we are talking in terms of the common reflector telescopes but the same applies for refractor telescopes. Aperture is simple, the size of the mirror or lens, usually given by its diameter. When viewing distant, faint objects a larger aperture is needed to collect as much light as possible from the selected section of the sky. The observed brightness of an object is directly proportional to the area of a telescope’s mirror. Because area is equal to π times the radius squared ( A= πR²). The brightness of an image will be the square of the diameter of the aperture. For example: Two telescopes. One with a 1m mirror, the other with a 5m diameter. The 5m telescope will have a brightness of 5² or 25 and the 1m will have a brightness of 1² or 1. Therefore, the 5m telescope will produce images 25 times brighter than the 1m telescope. Why should we care? The 5m telescope, in an astronomer’s terms, is “faster”. By faster, we are referring to the amount of time needed to take a picture. Look at it this way, when you take a picture in a dark room, your camera needs to leave the lens open for a longer period of time than if the picture was taken outside on a sunny day. This is because the photographic film needs time to collect enough photons of light to produce an image. Astronomers take lots of pictures of astronomical objects. With a brighter image they can take more pictures per unit of time and the movement created by the Earth’s rotation is not as much of a problem. The second advantage of large telescopes is angular resolution. Resolution is the ability to distinguish between two objects close together in a field of view. Angular resolution refers to how many arc seconds of distance between two objects can exist and the observer still can see them as two separate objects. One of the limiting factors on resolution is diffraction. Diffraction is the tendency of light to bend around corners. When light enters a telescope, even a perfect mirrored one, the rays spread out a bit creating some fuzziness. This fuzziness is caused by a loss of resolution. The degree of fuzziness determines the angular resolution of a telescope. Further, the amount of diffraction is proportional to the wavelength of the radiation divided by the diameter of the mirror. Angular Resolution = 0.25 Wavelength (um) / mirror diameter (m)

(arc seconds)

Where: 1um (1 micron) = 10^-6 meters

1 nanometer (nm) = 10^-9 meters

100nm = 0.1um

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Atmospheric Blurring

Stars twinkle. This change in the rays of light is due to the Earth’s atmosphere. Because the light, if refracted, the star twinkles. Atmospheric turbulence has a lesser effect on light of longer wavelengths, but the atmosphere sometimes raises havoc with ground based observations. Astronomers refer to “seeing” as the effects of the atmosphere on observing. One wants a night where the “seeing” is good.

f / Ratio The f / Ratio of a telescope is the focal length divided by the aperture. The aperture would be the diameter of the lens or mirror. This is an important number, as it tells a lot about a telescope. The lower the f /Ratio, the faster or brighter the image will be. This would be a good telescope for deep space object observation, but getting a brighter image means that you loose some magnification. f / 6 and lower = deep space observation f / 7 to f /10 = mid range f / 11 and up = slow but good for planetary work Here is the formula for determining the f / Ratio of a telescope: f / ratio = focal length / aperture Questions: 1.) Which would give you a brighter image, an 8 inch f / 10 of an 8 inch f / 6? 2.) Which would provide more magnification a 6 inch f / 8 of a 6 inch f /5? 3.) Explain your above answers. 4.) Given three telescopes: a.) Focal length = 2000mm Aperture = 203mm b.) Focal length = 800mm Aperture = 60mm c.) Focal length = 450mm Aperture = 4 inches (convert) Calculate the f / Ratio for each. 5.) Suggest ways that you could compensate of avoid atmospheric blurring.

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6.) Calculate the angular resolution of a 1 meter aperture telescope observing at the following wave lengths. Blue Light 400nm Red Light 700nm Inferred 1000nm

Telescopes 1.) A pair of binoculars has the markings 7 x 50. What do the 7 and 50 mean? 2.) What is the focal length of a 5m f / 3.3 mirror on Mount Palomar? 3.) What determines the size of the image formed by a telescope? 4.) What is the essential difference between refractors and reflecting telescopes? 5.) Explain why what may appear to be a single star to the naked eye may resolve into two close stars using a telescope. 6.) What is the magnifying power of a telescope related to the focal length of a telescope itself and the focal length of the eyepiece? 7.) What is the magnifying power of a 150mm f / 8 telescope using a 12.5 mm eyepiece? 8.) How could you increase the magnifying power? 9.) What is the practical limit of useful magnification of any telescope, given its aperture in millimeters? 10.) Compare and contrast chromatic and spherical aberrations. 11.) What is interferometry, assuming you were a radio astronomer. 12.) Compare and contrast radio astronomy with visual astronomy. 13.) List the two spectral ranges in the Earth’s atmosphere for observational astronomy. 14.) Star A is red. Star B is blue. Which is hotter? Explain how you know. 15.) What do all electromagnetic waves have in common? 16.) List the advantages of radio astronomy. 17.) Why do we put telescopes in space? 18.) Give two reasons astronomers want bigger telescopes. 19.) What and where are the largest optical telescopes in use today?

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20.) How does the Earth’s atmosphere affect an optical image? 21.) What kind of objects are best observed with a radio telescope? 22.) Why are radio telescopes large? 23.) Interferometry solves what problem for radio astronomers? Explain. 24.) Are there any ground-based ultraviolet observatories? 25.) Why do astronomers observe objects at different wavelengths?

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Radiation

There are other types of telescopes, but before we can discuss them, we must first have a working knowledge of the electromagnetic spectrum. And before the spectrum can make sense, one needs to understand waves and radiation in general. Astronomers use the laws of physics and parts of the electromagnetic spectrum to gather information about stellar objects. Radiation is any way energy is transmitted through space from point A to point B with out a physical connection between these two points. Radio transmission is a form of radiation. Electromagnetic means that the energy is carried in the form of rapidly fluctuating magnetic or electric fields. Visible light is a form of electromagnetic radiation the human eye can detect. To humans, much of the electromagnetic radiation is invisible. Radio, infrared, ultraviolet waves, as well as x-rays and gamma rays exist, but escape detection by humans. All electromagnetic radiation travels in the form of waves. A wave is a way in which energy is transferred from one place to another without the displacement of the medium in which the wave moves through. Your bobber while fishing moves up and down as energy moves through the water in the form of a wave. Still, the bobber ends at the same place that it started. A wave is the transfer of energy. Waves have a pattern. Waves have parts. We can differentiate different waves by the differences in their construction. Below is labeled diagram of a wave. The wavelength is the distance from the crest to crest or trough to trough. Or one can think of wavelengths as the distance a wave takes to repeat itself. The maximum displacement from the rested state is called the amplitude. The number of wave crests passing a given point per unit time is called the wave’s frequency. wave frequency = 1 / wave period Frequency is expressed in cycles, or crests, per second. The unit is the Hertz (Hz). If a wave has a period of 5 seconds then: Frequency = 1 / 5 sec. Frequency = 0.2 Hz A wave moves one wavelength in one wave period. Therefore: Wave length x Frequency = Velocity If our above frequency of 0.2 Hz wave had a wavelength of 0.5m, its velocity would be: 0.5 m x 0.2 Hz = 0.1m/s

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Wavelength and wave frequency are inversely related. If you double the wavelength and remain at the same velocity, frequency must be halved.

Visible Light

White light can be spread into its constituent colors by a prism. What makes red light? What makes violet light? Red is because of the wavelength. The wavelength of red light is 700nm, violet 400nm. The other colors have wavelengths between 400 and 700nm. The human eye is most sensitive to the middle wavelengths about 550nm. Visible light is but a small fraction of the electromagnetic radiation spectrum. But like all radiation waves, it needs no medium to travel through. Sound waves need air to travel. No air, no sound. Radiation waves need no medium.

The Electromagnetic Spectrum

Enclosed you will find a diagram depicting the entire electromagnetic spectrum. Please note that as the frequency and wavelength or inversely related. As the wavelength gets longer, the frequency decreases. Also note that the visible light spectrum is but a small fraction of the entire spectrum. The increments of change on the spectrums are not in 10, but factors of 10. At the long wavelength, low frequency end of the spectrum one will find the radio and infrared radiation. AM, FM, TV are all in the radio band of the spectrum. Infrared is heat. Shorter wavelengths are characteristics of ultraviolet, x-ray, and gamma ray radiation. Here is an example of the electromagnetic spectrum related to a common occurrence. You place a pot on the stove and turn on the burner. As the pot absorbs energy it emits some energy at the radio frequency. You cannot detect this, but with the pot left on the stove, you can feel the next area of the spectrum, namely heat. You are at the infrared zone now. Leaving the pot on the stove, it starts to glow red; then yellow, then blue. You have moved into and through the visible light portion of the electromagnetic spectrum. The Earth is bombarded continuously by electromagnetic energy from space. Only a fraction of the radiation reaches the surface because the Earth’s atmosphere. Opacity is the opposite of transparency. The Earth’s atmosphere blocks most of the radiation. The extent to which radiation is blocked is referred to as the opacity of the atmosphere. The Earth’s atmosphere allows visible and radio wavelength from space through and to some lesser extent some ultraviolet and infrared wavelength energy. Most electromagnetic energy is absorbed by the atmospheric gases. Water vapor and oxygen absorb wavelengths of less than a centimeter while carbon dioxide absorbs infrared radiation.

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Source: Chaisson, Eric. Astronomy today. McGraw Hill. 4th Edition.

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Doppler Effect

As an ambulance travels down the road you notice that the pitch gets higher as it nears you and then lowers once it has passed. The same effect happens when a train passes. This change in pitch is the result of the Doppler Effect. What causes the pitch to change is a change in the frequency. As the ambulance approaches you the sound waves are compressed. The intervals, or frequency, between the waves diminish and the pitch rises. When the ambulance passes, the sound waves are stretched out relative to you and the frequency decreases. The pitch goes down. If you could measure the rate of the change in pitch, you could calculate the speed of the ambulance. In the same way, electromagnetic radiation can be compressed or stretched, exhibiting the Doppler Effect. The radiation of an object approaching you is compressed into a higher frequency or shorter wavelength, and is said to be blue shifted. Redshifting occurs as an object moves away because the frequency is decreased and the wavelength is increased. To – Blue Away – Red Shifted The Doppler Effect applies to the entire electromagnetic spectrum and is used in astronomy to measure the movement of stars and galaxies. Astronomers use the spectral lines of the elements to determine the blue or red shifting of the stars.

The Doppler Effect

A Familiar Example Heard an ambulance go by recently? Remember how the siren's pitch changed as the vehicle raced towards, then away from you? First the pitch became higher, then lower. Originally discovered by the Austrian mathematician and physicist, Christian Doppler (1803-53), this change in pitch results from a shift in the frequency of the sound waves, as illustrated in the following picture.

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As the ambulance approaches, the sound waves from its siren are compressed towards the observer. The intervals between waves diminish, which translates into an increase in frequency or pitch. As the ambulance recedes, the sound waves are stretched relative to the observer, causing the siren's pitch to decrease. By the change in pitch of the siren, you can determine if the ambulance is coming nearer or speeding away. If you could measure the rate of change of pitch, you could also estimate the ambulance's speed.

By analogy, the electromagnetic radiation emitted by a moving object also exhibits the Doppler effect. The radiation emitted by an object moving toward an observer is squeezed; its frequency appears to increase and is therefore said to be blueshifted. In contrast, the radiation emitted by an object moving away is stretched or redshifted. As in the ambulance analogy, blueshifts and redshifts exhibited by stars, galaxies and gas clouds also indicate their motions with respect to the observer.

The Doppler Effect In Astronomy In astronomy, the Doppler effect was originally studied in the visible part of the electromagnetic spectrum. Today, the Doppler shift, as it is also known, applies to electromagnetic waves in all portions of the spectrum. Also, because of the inverse relationship between frequency and wavelength, we can describe the Doppler shift in terms of wavelength. Radiation is redshifted when its wavelength increases, and is blueshifted when its wavelength decreases.

Astronomers use Doppler shifts to calculate precisely how fast stars and other astronomical objects move toward or away from Earth. For example the spectral lines emitted by hydrogen gas in distant galaxies is often observed to be considerably redshifted. The spectral line emission, normally found at a wavelength of 21 centimeters on Earth, might be observed at 21.1 centimeters instead. This 0.1 centimeter redshift would indicate that the gas is moving away from Earth at over 1,400 kilometers per second (over 880 miles per second).

Shifts in frequency result not only from relative motion. Two other phenomena can substantially the frequency of electromagnetic radiation, as observed. One is associated with very strong gravitational fields and is therefore known as Gravitational Redshift . The other, called the Cosmological Redshift, results not from motion through space, but rather from the expansion of space following the Big Bang, the fireball of creation in which most scientists believe the universe was born.

Spectroscopy

Starlight is composed of various wavelengths of light. Astronomers can determine much about the source of the light by analyzing the light itself. Spectroscopy is the analysis of the spectra of the light.

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Spectra are of three basic types. Each type is produced by different conditions. Which are as follows: 1.) Continuous spectrum is all of the colors that make up visible light. 2.) Emission spectrum is a pattern of dark lines, each from a different wavelength, also called a bright-line spectrum. 3.) Absorption spectrum is a pattern of dark lines across a continuous spectrum, also called a dark-line spectrum.

Emission and Absorption Lines Homework for tomorrow's class

People have long known that the stars are far, far away; in the nineteeth century, astronomers finally measured the distances to a few nearby stars with reasonable accuracy. The results were so large -- thousand of trillions of miles -- that most people figured we'd never be able to visit them or learn much about them. After all, we can't go to a star, grab a sample, and bring it back to earth; all we can do is look at light from the star. In fact, at least one prominent philosopher and scientist went on the record as saying that we'd never be able to figure out their compositions.

Of all objects, the planets are those which appear to us under the least varied aspect. We see how we may determine their forms, their distances, their bulk, and their motions, but we can never known anything of their chemical or mineralogical structure; and, much less, that of organized beings living on their surface ...

Auguste Comte, The Positive Philosophy, Book II, Chapter 1 (1842)

(Comte refers to the planets in the quotation above; he believes that we can learn even less about the stars)

But, it turns out, light from the star encodes a wealth of information about the physical state of its outer atmosphere. Light is produced in the inner regions of a star and works its way out to the "surface" -- which is really a part of the gaseous atmosphere called the

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photosphere. Photons produced in the photosphere have a good chance to escape outwards into space and, eventually, reach us. As photons fly through the outermost layers of the stellar atmosphere, however, they may be absorbed by atoms or ions in those outer layers. The absorption lines produced by these outermost layers of the star tell us a lot about the chemical compositition, temperature, and other features of the star.

Today, we'll look at the processes by which emission and absorption lines are created. We'll also do a little bit of analysis, but leave most of it for a later day...

Emission-line spectra

Low-density clouds of gas floating in space will emit emission lines if they are excited by energy from nearby stars. Planetary nebulae, for example, are the remnants of stars which have gently pushed their outer envelopes outwards into space. Some of them are very pretty:

See Astronomy Picture of the Day for Oct 31, 1999

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See Astronomy Picture of the Day for March 21, 1999

The hot central stars which remain irradiate these wispy shells of gas with high-energy ultraviolet photons, which excite the atoms in the gas and cause it to glow. The spectrum of a planetary nebula reveals almost nothing but very strong, narrow emission lines:

Remember that 10 Angstroms = 1 nm, so 4000 Angstroms = 400 nm = blue light ...

What exactly did I mean by the phrase excite the atoms in the gas? And what does that have to do with these narrow emission lines? Let's take a look at the individual atoms in the gas around a planetary nebula....

Atomic energy levels and transitions

Individual atoms consist of a nucleus of positive charge surrounded by one or more negative particles called electrons. To a rough approximation, the electrons circle the nucleus, somewhat as planets circle the Sun.

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Q: What is the force which keeps planets in orbit around the Sun? Q: What is the force which keeps electrons in "orbit" around the nucleus?

The answers

Unlike the orbits of planets and asteroids around the Sun, which may be any size, the orbits of electrons in atoms turn out to obey a rather peculiar set of rules.

1. Only orbits of certain particular radius are permitted 2. Each orbit has a different potential energy: small orbits have low potential energy,

large orbits have high potential energy 3. Electrons may jump between any two orbits, but do so instantaneously;

o for the electron to jump upwards, to a larger orbit, something must provide exactly the right amount of energy to the atom

o for the electron to jump downwards, to a smaller orbit, the atom must get rid of exactly the right amount of energy

So, for example, one particular atom might have orbits with energy levels like this:

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In this case, the energy difference between the second and first orbit is Δ E = 6 - 1 = 5 units. We'll discuss details of the units in a moment. Now, if a photon of 5 units of energy happens to run into this atom, it might be absorbed by the atom, exciting the electron from the first orbit to the second orbit.

Before ...

... and after.

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Notice that the photon has disappeared.

Once you have excited an atom, all you have to do is wait a bit; eventually, the atom will jump back down to a lower energy state, emitting a photon itself.

The energy of this emitted photon is exactly equal to the difference in atomic energy levels between the initial and final states. In this example, the emitted photon would have 5 units of energy.

Because each type of atom has its own unique set of energy levels, each type of atom will emit light with a different set of energies. And, given the relationship between the energy E of a photon and its wavelength λ (or frequency ν)

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that means that each type of atom will produce a set of emission lines at its own unique wavelengths.

Example: the spectrum of hydrogen

For example, consider hydrogen, the simplest (and most common) element in the universe. It consists of a single proton in its nucleus, around which a single electron orbits.

The energy levels of a hydrogen atom follow a regular pattern. The energy of level n is given by a simple formula:

Sometimes it helps to make a picture of the energy levels.

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We put the "ground state" level, n=1, at the bottom of the diagram. At the top, we put the level at which the atom will be ionized: if it gains this much energy, the electron flies off into space, never to return.

We can depict an atomic transition graphically by drawing a little ball on the diagram to represent the energy of the atom. If the atom drops from a high level to a lower one, it will emit a photon. The energy of the photon is equal to the difference between the initial and final energy levels.

Q: What is the energy of the photon emitted when a hydrogen atoms drops from n=2 to n=1?

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The answer

As mentioned earlier, the energy of a photon determines its wavelength. You can convert from one to the other via a formula

where h is Planck's constant and c is the speed of light. The combination h times c has the convenient value of 1240 eV*nm, so

Q: What is the wavelength of the photon emitted when a hydrogen atoms drops from n=2 to n=1? Could you see that photon with your eye?

The answer

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Q: What is the wavelength of the photon emitted when a hydrogen atoms drops from n=3 to n=2? Could you see this photon?

The answer

Transisions in which a hydrogen atoms drops down in energy to the second level are called Balmer transitions, after the scientist who first measured their properties very carefully. Since they occur in the visible portion of the spectrum, and they involve the most common element in the universe, they are one of an astronomer's most powerful tools. If you look again at the spectrum of the planetary nebula, you'll see several Balmer lines:

Remember that 10 Angstroms = 1 nm, so 4000 Angstroms = 400 nm = blue light ...

Other atoms have spectra which are more complex than that of hydrogen; there are no simple formulae describing their energy levels. Fortunately, many scientists have spent years measuring the wavelengths of light emitted and absorbed by almost every variety of atom (and ion, and molecule) you can imagine. You can look up the wavelengths for any particular material in one of several big compilations of spectral lines.

• Line Spectra of the Elements, by J. Reader and Ch.H. Corliss • Atomic spectral line list, by R. Hirata and T. Horaguchi • A revised version of the Identification List of Lines in Stellar Spectra (ILLSS)

Catalogue by R. Coluzzi

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Absorption lines

A high-resolution spectrum of the Sun shows many, many, MANY dark absorption lines:

Absorption lines are based on the same physical principle as emission lines: they involve an atom jumping from one particular energy level to another. In this case, however, the jumps must be upwards, from a low level to a higher one.

For example, if a photon of wavelength 121 nm happens to fly past a hydrogen atom in its ground state,

the hydrogen atom will absorb the photon and hop up to the n=2 level.

That means that if we look at a source of continuous radiation

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through a cloud of hydrogen gas, we will see a dark absorption line at 121 nm.

We see absorption lines in the spectra of ordinary stars like the Sun because the tenuous outer layers of the stellar atmosphere -- called the photosphere -- absorb some of the continuous light coming from the hot, dense interior.

The conditions needed to produce line spectra

Emission and absorption lines can tell us a great deal about a distant celestial source, but they only occur under certain conditions.

Emission lines from an element will appear if

• there are atoms of the element present • the atoms are in a low-density gas • the atoms are excited into a particular high energy level by some external source

Absorption lines from an element will appear if

• there are atoms of the element present • the atoms are in a low-density gas • the atoms spend most of their time in a particular low-energy level • the gas lies between us and a source of continous light (of all wavelengths)

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Homework for tomorrow's class

1. Print a copy of the spectrum of the planetary nebula PN G000.2+06.1, which is shown at the top of this lecture. On the printed copy,

o identify and mark the emission lines which are due to Balmer transitions of hydrogen atoms; you should be able to find at least 3 or 4

o for each of these lines, write down the initial energy level and the final energy level involved in the transition (i.e. for the line at 656 nm, you would write "initial n=3, final n=2")

2. Look at the stellar spectrum below.

o Estimate the temperature of this star. o Sodium atoms have the following energy levels: (sort of -- I've assigned

some new numbers) o o n energy (eV) o ------------------------- o 1 -5.14 o 2 -3.04 o 3 -1.96 o 4 -1.52 o -------------------------

One of the strongest lines in the spectrum above is due to a transition in sodium atoms. Which one is it? What is the wavelength, and what are the levels involved?

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For more information

• Looking for the source of some particular spectral line? Check out the Spectra of Gas Discharge page.

• You might also play with the MiniSpectroscopy Java Applet • The spectra of planetary nebula shown above come from a paper by Mantiega et

al., AJ 127, 3437 (2004)

Copyright © Michael Richmond. This work is licensed under a Creative Commons License.

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What causes each of these spectrums? The structure of the atom is what makes it possible. In the Bohr atom model, the nucleus contains protons and neutrons. Orbiting the nucleus are the negatively charged electrons. Because atoms usually have no charge, the number of protons equals the number of electrons. The electron orbit is at a fixed radius relative to the nucleus. For each element, there are a varying number of orbits. The energy needed to remove an electron from its orbit is called the binding energy. Each element also has a unique set of allowed electron orbits called energy levels. If an atom is chillin’, undisturbed, it is said to be in its ground state and has the least possible energy. It the right energy is supplied (think frequency and wavelength here) the electron will jump to a higher energy level. The atom is now in an excited state. When the electron goes back to the ground state, the previous absorbed energy is released in a packet of light called a photon. If enough energy is supplied electrons can be removed completely creating ions. Dark absorption lines are created when the atoms take in energy. Bright emission lines are created when the electrons return to ground state. Each element has unique absorption and emission lines. The same can be said for compounds. The Sun’s absorption spectrum was studied by Joseph von Fraunhofer in 1814. The darkest lines of the Sun’s spectrum are called Fraunhofer lines and they indicate what elements compose the Sun. Other stars can be classified according to their absorption spectrum. Source: http://www.creativecommons.org

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Questions: Electromagnetic Spectrum 1.) What is a wave? 2a.) What color has the shortest wavelength? 2b.) What is the shortest wavelength? 3.) List 6 forms of electromagnetic energy from the shortest to the longest wavelength. 4.) How many kilometers in 1 light year? 5a.) Which waves have a higher frequency than visible light? 5b.) Which waves have a lower frequency than visible light? 6.) What is the relationship between wavelength and frequency? 7.) Given the wavelength of an electromagnetic wave, one can determine the frequency. However, to determine the frequency, one must use the formula: speed of a wave = Frequency x Wavelength Why? 8.) Calculate the wavelength of a radio wave whose frequency is 100K Hz (k=1,000) 9.) A sound wave in water has a frequency of 256Hz and a wavelength of 5.77m. Find the wave’s velocity. 10.) What is the wavelength of 100M Hz? 11.) What is diffraction? 12.) What is special about c, the speed of light?

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Radio Astronomy As we have seen, on the surface of the Earth an astronomer can expect to detect the visible and radio wave lengths emitted from objects in space. These two areas of electromagnetic spectrum are called windows of observation. The first radio wave observation of astronomical value was made at a wavelength of 14.6 meters. FM radio and TV transmission occur around the 3 meter wavelength while AM radio has a wavelength of 300meters. Today, most radio observations are done between the wavelengths of 90cm and 7mm. Similar to optical telescopes, radio telescopes are either prime focus or Cassegrain reflectors. Radio telescopes are large. Why? Remember that angular resolution is proportional to the wavelength divided by the aperture diameter. Angular Resolution = Wavelength / Diameter So for a radio telescope to have a good resolution at the large wavelengths of radio, the diameter must be large. Also, if the telescope is to detect faint signals the collection area or reflector must be large. Diffraction is also a problem. Remember that the longer the wavelength, the greater the diffraction. Angular resolution of a single radio telescope can approach 20 arc seconds when the wavelength is about 3cm. How a radio telescope works: Lets look at how the radio telescopes of the Very Large Array work. There are four basic components: A reflector, sub-reflector, feed, and receiver compose a radio telescope. As a radio source emits radiation and it travels to the Earth’s surface, it strikes the radio telescopes reflector. Some would call this the dish. An astronomer wouldn’t. The reflectors are a parabola. A parabola is defined as a set of points in the plane that are equidistant from a point (the focus) and a line (the directrix). The important part of parabolas for astronomers is that a parabola has a focus. A focus is a point where incoming waves will be concentrated to after bouncing off the reflector. If you have a dish for TV at home take a look at it tonight. It is a parabola. The focus point is where that little receiver is held above the dish. For a radio telescope astronomers place a structure called the sub-reflector at the focus. The sub-reflector redirects the radiation back down into the middle of the reflector where the electromagnetic waves enter the feeds. At the VLA, these feeds are commonly referred to as feed horns. A receiver is located behind the feeds just like in a Cassegrain optical telescope. For that matter, the radio telescope is very similar to a Cassegrain optical telescope, only larger and operating at a different wavelength. The receiver amplifies the signal, and is built such that the incoming signal remains proportional, even after amplification. This allows the image to remain true, relative to the emission received. The signals are then

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transferred to a computing area where, through the process of modern computing, an image is produced. Radio astronomers have taken the radio wavelength section of the electromagnetic spectrum and have further divided it into bands. Below is a list of the bands and their wavelengths and frequencies. Band Wavelength Frequency P-Band 90cm 327 MHz L-Band 20cm 1.4 6Hz C-Band 6.0 cm 5.0 6Hz X-Band 3.6cm 8.5 6Hz U-Band 2.0cm 15. 6Hz K-Band 1.3cm 23 6Hz Q-Band 7mm 45 6Hz

What do Radio Astronomers “Look” At? Apparent magnitude is used by optical astronomers when they look at the stars. This brightness factor, in the terms of physics is called the flux density of the object. The flux density, similar to brightness, is the measure of the power received from an object per unit frequency, per unit of area. It turns out that most of the stars are not particularly strong emitters of radio frequency waves. Some are, but most, even our Sun, aren’t. But the gasses of space emit big-time at the radio frequency. Radio astronomers observe what is not visible.

Advantages of Radio Astronomy

We have highlighted the disadvantages of radio astronomy; poor angular resolution of a single telescope. But radio astronomy has many advantages. 1.) Observations can take place 24 hours a day. The Sun is a weak radio source. 2.) Clouds? No problem. Radio telescopes and detect radio waves even through the rain and snow. 3.) Some of the strongest sources of radio emissions emit little or no visible light. The only way to study them is at the radio wavelength. 4.) Although visible light may be absorbed or distorted by interstellar matter, radio waves are not. Parts of the universe that cannot be seen visibly can be studied with a radio telescope.

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Source: http://www.nrao.edu

Interferometry All astronomers detest poor angular resolution. Radio astronomers have overcome poor angular resolution by using a technique called interferometry. Interferometry is the practice of using two or more radio telescopes, in tandem, to observe the same object at the same time and at the same wavelength. The VLA uses interferometry and has the ability to use up to 27 radio telescopes in unison. As each telescope receives radiation, the signals are sent to a central computer. The computer combines and stores the data. The trick is to see how the waves interfere with each other when added together. If the waves are in phase, they combine constructively to form a stronger signal. If the signals are out of phase with one another, they combine to cancel each other out. Eventually, as the telescopes track their target, a pattern emerges. With the voodoo of extensive computer processing, the pattern is translated into a high-resolution image. Remember that angular resolution is equal to the wavelength divided by the aperture. With interferometry, that aperture, or diameter of the mirror becomes the distance between the radio telescopes. Let’s now call the aperture the baseline. We will define the base like as the distance between radio telescopes. Angular Resolution = wavelength / Base line length

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The further you spread the telescopes, the more angular resolution you achieve. How much angular resolution can be achieved? Well, the VLA has four formations, A, B, C, and D, where the maximum separations are: A - 36km B - 10km C - 3.6km D - 1km With a base line of 36km, the VLA can reach a resolution of 0.04 arc seconds at a wavelength of about 7mm. Want even better resolution? Meet the VLBA; The Very Long Baseline Array. This array has radio telescopes spanning the distance from the east coast to Hawaii, including one in Pietown, N.M.

Infrared Telescopes

First built in the 1960’s, these telescopes operate like optical reflectors, but with a heat detector at the prime focus. Cooled to about 2K they detect infrared waves from space. Because water and carbon dioxide in the atmosphere absorb infrared rays, most large infrared telescopes are located on mountaintops. http://sofia.arc.nasa.gov http://sirtf.caltech.edu www.ipac.caltech.edu

Ultraviolet, X-Ray, and Gamma Rays

High-energy astronomy started in the 1960’s, with telescopes above Earth’s atmosphere. High-energy telescopes collect and focus incoming radiation where detectors record its intensity, energy, duration, and direction. Computers assimilate the data and manipulate it to form false color images; sort of a paint-by-numbers concept. This generates a picture of objects that can’t be seen visually. http://galex.caltech.edu http://chauclra.harvard.edu

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Galaxies

A galaxy is a large collection of stars, gas, and dust held together by mutual gravitation. Edwin Hubble (think telescope) was the first to categorize galaxies from Mount Wilson Observatory in California. Hubble placed galaxies into four basic groups: a.) Spirals b.) Barred Spirals c.) Elipticals d.) Irregulars These classifications are based solely on appearance. The classification is referred to as the Hubble classification scheme. Spiral Galaxies, like the Andromeda, contain a flatted galactic disk with spiral arms, a central galactic bulge, and a halo of faint, old stars. Most stars are found in the middle, or galactic nucleus of the galaxy. Hubble went further in classifying galaxies by adding the size of the central bulge. Using “a” for the largest galaxies, and “c” for the smallest, the spiral galaxies have three classifications denoted by the following: Sa Sb Sc Sa galaxies, with a large central bulge tend to be tightly wrapped with almost circular arms. Sb have more openness to their arms while Sc, the smallest of bulges, have loose poorly defined arms. Also, the arms tend to have, “knots”, or clumps, as they become more open. Because the halo of most galaxies glows reddish, it is assumed that the older stars reside there while the outer arms, being blue and white, contain the B and O type stars. The arms, rich in gas and dust, are the nurseries for stars. Barred spiral galaxies differ from ordinary spirals in that they contain a “bar” of matter that passes through the center, and to the arms of the galaxy. The arms project from the bars and not from the center of the galaxy. Barred spiral galaxies are also sub-divided into groups depending on the size of the central bulge. The classifications are denoted as follows: SBa SBb SBc Astronomers cannot differentiate the difference in galaxies if the view is edge-on to the observation. Our own Milky Way, with its elongated bulge suggests that we live in a barred spiral galaxy, probably an SBb or a SBc.

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Elliptical galaxies have no spiral arms and no flattened galactic disk. There is little internal structure to an elliptical galaxy. These galaxies are further sub-divided by how elliptical they are. The most circular are denoted by E0 and the most elongated are denoted by E7 An irregular galaxy classification is a depository classification for galaxies that do not fit into the above classifications. Irregulars have a lot of young blue stars, but lack a regular structure. They are further divided into Irr1 and Irr2 galaxies. Irr1 galaxies look like bent spirals while Irr2, also misshapen, appear explosive. The Magellanic Clouds are a pair of Irr1 galaxies. Some astronomers suggest, although it has not been proven, that galaxies undergo an evolutionary path. It is suggested that they start as elliptical, and because of interactions, develop into spiral of irregular galaxies.

Star Populations and Stellar Movements

Many stars move through a galaxy, many move in a group held together by their mutual gravitational attraction. These groups are called star clusters. It is thought that all of the stars in a cluster formed about the same time in the same gigantic cloud, because all of the stars are about the same age. Star clusters come in two basic flavors: open, or galactic clusters that are found in the spiral arms. They are relatively young, hot, and highly luminous. In the spherical region around the disk, called the halo, astronomers have found globular clusters. These are the older stars.

Population 1 and 2 Stars

Yet another classification of stars in a galaxy is that of Population 1 and 2. Population 1 stars are found in the arms of the galactic disk and are the hottest and most luminous stars. Also, they contain high amounts of heavier elements. Population 2 stars are found near the galactic nucleus. They are older and composed almost entirely of hydrogen and helium.

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Data < Galaxy Types < back

Basic Galaxy Properties by Type SPIRAL/BARRED SPIRAL

(S, SB) ELLIPTICAL(E) IRREGULAR (IRR)

Shape and structural properties

Highly flattened disk of stars and gas, containing spiral arms and thickening to a central bulge; Sa and Sba galaxies have largest bulges, the least obvious spiral structure, and roughly spherical stellar halos.

SB galaxies have an elongated central "bar" of stars and gas

No disk Stars smoothly distributed through an ellipsoidal volume ranging from nearly spherical (E0) to very flattened (E7) in shape

No obvious substructure other than a dense central nucleus

No obvious structure; Irr II galaxies often have "explosive" appearance

Stellar content

Disks contain both young and old stars; halos consist of old stars only

Contain old stars only

Contain both young and old stars

Gas and dust

Disks contain substantial amounts of gas and dust; halos contain little of either

Contain little or no gas and dust

Very abundant in gas and dust

Star formation

Ongoing star formation in spiral arms

No significant star formation during the last 10 billion years

Vigorous ongoing star formation

Stellar motion

Gas and stars in disk move in circular orbits around the galactic center; halo stars have random orbits in three dimensions

Star have random orbits in three dimensions

Stars and gas have very irregular orbits

Source: http://www.astronomynook.com/galaxy-types.htm

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Questions: Galaxies 1.) Define a galaxy. 2.) Compare and contrast open galactic and globular clusters. Location, age and color. 3.) Why is the composition of the interstellar medium important to the theory of stellar evolution? 4.) Describe the classification system for galaxies. 5.) What is our local group? 6.) Diagram and label the parts of the galaxy.

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Local Group

A common astronomical term used is: our local group. Our local group is composed of neighboring galaxies within 1Mpc of the Milky Way. There are 45 galaxies in our local group. Three of the 45 galaxies are spiral galaxies (the Milky Way, Andromeda, and M33). The remainder are dwarf irregulars and dwarf ellipticals. The group is held together by mutual gravitational attraction into a group called a galaxy cluster.

Hubble’s Law

Do the galaxies and galactic clusters move? Is there motion random? Research at the turn of the century indicates that their motion is very orderly. In 1912 V. Slipher, working with P. Lowell discovered that virtually every spiral galaxy had a red shifted spectrum. The galaxies were moving away from us, or receding from our galaxy. Except for a few nearby systems, all galaxies were found to be receding. The recessional velocity of the galaxies versus the distance was plotted on a graph. If one studies the graph some surprising conclusions emerge. One will notice that as the distance increases, so does the recessional velocity. This means that the most distant galaxies are moving away faster than the closest galaxies. There is a direct correlation between velocity and distance. This diagram is called the Hubble diagram, and from it one of the pillars of astronomy can be drawn: Hubble’s Law. Hubble’s Law states that the rate at which a galaxy recedes is directly proportional to its distance to us. The universal recession described by the Hubble diagram and law is called the Hubble Flow. The bottom line is that the universe is expanding. Let’s be clear about the concept of expansion. It is not meant that the quantity of matter is expanding for the law of conservation of mass prohibits that idea. Instead, it is meant that the distance between objects in the universe is expanding. Astronomers distinguish the recessional red shift of the universe from a red shift within an object, like a galaxy, by referring to the universe’s red shift as the cosmological red shift. Because Hubble’s Law is based on observational results, it is empirical by nature. But it does pose some interesting questions about the origin of the universe. With the concept that recessional velocity and distance are proportional, one has to wonder what is the constant of proportionality? Or what is the slope of our line. The constant is referred to as Hubble’s constant, and the equation can be written as follows: Recessional Velocity = Ho x Distance Where: Ho = Hubble’s Constant recessional velocity = velocity of movement away in km / s distance = distance in millions of parsecs Astronomers continue to refine Hubble’s Constant, but the current agreed upon value is about 65 km/s

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Questions: Hubble’s Law 1.) Using the formula for Hubble’s constant prove that the slope of the line in Hubble’s Law is indeed Hubble’s constant. 2.) Hubble’s constant is about 65 km/s. What does this really mean? 3.) Some galaxies in our local group are blue shifted. How can this be if Hubble’s Law is true? 4.) Given the following galaxies determine their recessional velocity. Galaxy Distance (million parsecs) A 3 B 102 C 2 x 10² 5.) Given the following velocities, determine the distance. Galaxy Velocity (km/sec) A 130 B 2 C 43

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Messier Objects

g for which were comets. To e a big dog astronomer in his day was to find a comet.

inal 110 objects are referred to in astronomy by their number preceded by a capital .

xamp

From the years 1758 to 1782, a French astronomer named Charles Messier made a list of about 100 objects he observed in the night sky. He did such so that he wouldn’t confuse these diffuse looking objects for what he was really lookinb What Messier ended up compiling was a list of nebulae, star clusters, and galaxies. It was the first list of deep sky objects and is still in use today, with additions. Today, the origM E le: M 31 is the Andromeda Galaxy.

ross an bject, and desire to se what it looks like, it is only a computer search away.

There are images for all Messier objects. If, in your study, you run aco

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Common Names for Messier Objects note the most recent copy of the list arranged by Messier numbersAlso .

ct You are invited to supply all additional common names you know for them ! Just contame.

Common names for the Messier objects (as well as other deep sky objects) are usually assigned for either the constellation where the object is situated, or to honor the

way easy to remember; but there are

Some of the names often carry the adjective "Great" or something alike; I omit those reasonability.

"Andro

discoverer, or to desribe the object's appearance in ano rules for assigning common names.

Names used in various sources:

forms of names formeda Galaxy" M31

"Barbell Nebula" M76 (also Little Dumbbell Nebula, Butterfly Nebula, or Cork Nebula). Mike

it "Apple Core Nebula". "Beehiv

Frazier callese Cluster" M44 (also Praesepe or Manger)

"Blackeye Galaxy" M64, also sometimes called the "Sleeping Beauty Galaxy".

"Bode's Galaxy" or "Bode's Nebula" M81 (Murdin/Allen/Malin 1979)

"Butterfly Cluster" M6 (`Splendors of the Heavens', Phillips/Steaphenson 1923). According to JBondono, also

eff M93 is also sometimes called by this name.

ebula" "Butterfly NM76 (also Little Dumbbell Nebula, Cork Nebula, or Barbell Nebula). Mike

"Apple Core Nebula". "Cetus

Frazier calles it A" M77

"Checkmark Nebula" M17 (also Omega, Swan, Horseshoe, or Lobster Nebula)

"Cigar Galaxy" M82. Brought to my attention by Tom Polakis.

"Cork Nebula" M76 (also Little Dumbbell Nebula, Butterfly Nebula, or Barbell Nebula). Mike

s it "Apple Core Nebula". "Crab N

Frazier calleebula"

M1 (Rosse 1844) "Delle Caustiche"

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M24. The Sagittarius Star Cloud. A Milky Way Patch containing the open cluster NGC 6603

"de Mairan's Nebula" M43. Part of the Orion Nebula

"Diablo Nebula" M27, the Dumbbell Nebula. Contributed by Jeff Bondono, also Sky Catalog 2000.

" "Double-Headed ShotM27, the Dumbbell Nebula. Contributed by Jeff Bondono, also Sky Catalog 2000.n Nebula"

"Drago

e Lagoon Nebula M8Name for a part of th (Sky Catalog 2000). "Dumbbell Nebula"

M27. Jeff Bondono found that it is also called "Diablo Nebula" or "DoublShot", J.R. Freembell Nebula, Little"

e-Head an heard "Apple Core Nebula".

"DumbM76 (also Cork, Butterfly, or Barbell Nebula). Mike Frazier calles it "Apple Core

he name "Little Dumbbell Nebula" is most common, e.g. Sky

ames like no other: It has also two NGC

Nebula". TCatalogue 2000 NB: This object seems to attract nnumbers: 650 and 651.

"Eagle Nebula" IC 4703 associated with the star cluster M16 (also "Star Queen Nebula")

luster" "Hercules Globular CM13

"Horseshoe Nebula" M17 (also Omega, Swan, Lobster, or Checkmark Nebula) lass Nebula" "Hourg

rt of M8Brightest Pa , the Lagoon Nebula "[St.] K

utiful spiral galaxy M99atherine's Wheel" The bea . Referred by this name by Francis Jacob (1895) -

municating. thanks to Bob McGown and Dareth Murray for com"Lagoon Nebula"

M8. Its center contains "The Hourglass Nebula" (A.D. Thackeray 1956). riplet" "Leo TM65, M66 and NGC 3628 form this physical trio

ebula" "Little Dumbbell NM76 (also Cork, Butterfly, or Barbell Nebula). Mike Frazier calles it "Apple CNebula". The name "Little Dumbbell Nebula" is most common, e.g. Sky Catalogue 200

ore

0 "Lobster Nebula"

M17 (also Omega, Swan, Horseshoe, or Checkmark Nebula); thanks to Steve r this contribution, a common name for M17 on the Southern

e)

Mencinsky fohemisphere.

"Manger" (PraesepM44 (also Beehive Cluster)

"Milky Way Patch" M24 (also "Delle Caustiche"). Star cloud containing the open cluster NGC 6603

" "Omega NebulaM17 (also Swan, Horseshoe, Lobster, or Checkmark Nebula)

79

"Orion Nebula" M42. M43 is also a part of it. ebula" "Owl NM97 eel Galaxy" Two, or even th

"Pinwhree, galaxies (all in Messier's catalog) share this name:

M101. More common [Murdin/Allen/Malin 1979, Sky Catalogue 2000,Observer's Handbook]

RASC

M33, the Triangulum Gadistinguishing

laxy [Burnham, RASC]; take "Triangulum Pinwheel" for

M99 [RASC]; take "Coma Pinwheel" or "Virgo Cluster Pinwheel" for guishing, if needed. M99 is also, more properly, referred to as "St.

rhaps more common for M101 because it has no other name. The name for M33 is Burnham.

distinKatherine's Wheel." The name is peonly major source having this

"Pleiades" M45 (also Subaru or the Seven Sisters)

"Praesepe" (Manger) M44 (also Beehive Cluster)

"Ptolemy's Cluster" M7 (Ptolemy mentioned it 138 AD, hf)

Rosse "Question Mark" of Lord M51 (also The Whirlpool Galaxy) ebula" "Ring N

M57 "Sagittarius Star Cloud"

M24 (also "Delle Caustiche"). A Milky Way Patch containing open star cluster NGC 6603.

Satellite Galaxies of M31 M32, M110

"Seven Sisters" M45 (also Subaru, the Pleiades)

"Sleeping Beauty Galaxy" M64, also the Blackeye Galaxy.

ter of M87"Smoking Gun"

Name for the active cen (Virgo A). Nasa/STScI. "Sombrero Galaxy"

M104 "Southern Pinwheel Galaxy"

M83 "Spindl

02[?]e Galaxy" M1 = NGC 5866 (hf, Sky&Telescope 7/95 p. 51). Name shared with NGC 3115

"Star Queen Nebula" 3 associated with the star cluster M16IC 470 (also "Eagle Nebula")

"Subaru" M45 (also the Pleiades or Seven Sisters)

"Sunflower galaxy"

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M63 "Swan Nebula"

M17 (also Omega, Horseshoe, Lobster, or Checkmark Nebula) er"

r of young stars in M42"Trapezium Clust

Cluste , the Orion Nebula Galaxy" "Triangulum

M33 (also "Pinwheel", that shared with M101) Nebula"Trifid " M20

"Virgo A" M87 in the center of the Virgo cluster. Its active center is called "The Smoking Gun"

"Whirlpool Galaxy" M51 (Lord Rosse's "Question Mark")

"Wild Duck Cluster" M11 (Smyth)

"Winnecke 4" (WNC4) M40, the Double Star in Ursa Major

"WNC 4" (Winnecke 4) M40, the Double Star in Ursa Major

Propositions for further names: Many o r astronomer Jeff f these proposed names have been contributed by amateuBondono -- thanks !

Two nebulae share this name (the Dumbbell and the Little Dumbbell Nebula, or should

"Apple Core Nebula"

we say the "Normal" and Little Dumbbell ? :-) ) M27, the Dumbbell Nebula. Contributed by J.R. Freeman, common in SoutCalifornia.

hern

M76, the Little Dumbbell, Cork or Butterfly Nebula. This is Mike Frazier's name

ike no other: It has also two NGC and 651.

"Blowd

for it. NB: This object seems to attract names lnumbers: 650ryer Galaxy" M100. Contributed by Devon J. Moore - because it is pinwheel-shaped and that

it's in Coma, "The Hair Constellation."

"Butterfly Cluster"M93. Contributed by Jeff Bondono. This name is shared with M6, see above.

"Cat's Eye Galaxy" M94. Contributed by Devon J. Moore.

"Cooling Tower" M29. Contributed by Jeff Bondono. Shaped Cluster" "Heart-M50. Contributed by Jeff Bondono.

"Maytag Galaxy"

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M33; humourous American name for the Triangulum galaxy, as M51, the orgeous face-on spirals, and "Whirlpool"

h washing machines. Contributed by J.R. Freeman. "Perfec

Whirlpool galaxy, and M33 are both gand "Maytag" are bott Spiral Galaxy" M74 (Gemini Press Release 2001-2). eel Cluster" "PinwhM36. Contributed by Jeff Bondono. d-Pepper Clusters" Jeff Bondono has proposed these names for a collection of open clusters, namelyM11, M37, and M52. Originally we had attributed them for terrestrial seasonsthat they had difrespectively. This has caused protest, so that we decided t-- sorry to all who have enjoyed them, but, as Jeff has put it: contain only generally accepted propositions. But he has now pro

"Salt-an

, so ferent names on the Southern and the Northern hemisphere,

o drop these names now This list should

posed naming onth names, and I could imagine to name them after their homing them by m

constellations: M11 "July Salt-and-Pepper", "Scutum Salt-and-Pepper" M37 "January Salt-and-Pepper", "Auriga Salt-and-Pepper" M52 "October Salt-and-Pepper", "Cassiopeia Salt-and-Pepper"

"Spiral Cluster" M34. Contributed by Jeff Bondono.

"Starfish Cluster" M38. Contributed by Jeff Bondono.

"Surfboard Galaxy" M108. Propo

"Vacuum Cleaner Gasition by Scott D. Davis. laxy"

09M1 . Proposed by Devon J. Moore. • Look at a list of some more Common Names for Deep Sky Objects

Hartmut Frommert Christine Kronberg [contact]

Last Modification: July 15, 2006

Source: http://www.seds.org/messier/indexes.html

82

Constellations

Constellations, historically speaking are groupings of stars that outline an image. The age was usually that of a character or item told in a story, or myth. Common

a

s, Greeks, Romans, Chinese, and ative Americans all have stories that are told through the stars in the sky.

.

The Zodiac is a band 18-d ptic. The constellations that fall into this space number 12 and are ca ed the constellations of the Zodiac, also

imconstellations associated with mythology are Cancer, Hercules, and Orion only to namefew. There are 88 recognized constellations from the contributions of many cultures, dating back to 3000 B.C. The Mesopotamians, EgyptianN Some common constellations such as the Big Dipper are not constellations at all. The Big Dipper is actually part of the constellation Ursa Major (Big Bear). The Big Dipper isproperly referred to as an asterism or grouping of stars

egrees wide that is centered on the eclill

called the signs of the Zodiac. Due to astrology, it was thought that these constellationsheld sway in the turn of human events. Not so at all.

The Importance of the Constellations

Once humans settled down to farming, it didn’t take long for the farmers to determine

onstellations. The area directly associated, and

round the constellations are said to be “in” the constellation. Therefore, an object can be . For

ot include the essier objects mentioned above.

e, ta

ar called Rigel, a blue super giant, magnitude of 0.2. The delta star also has a common

that the seasons needed to be predicted. It was observed, for instance that the constellation Virgo starts to appear about the same time as spring. The constellation Orion starts to appear in the fall. Early civilizations, using the constellations, could predict the seasons. They functioned as a calendar. Today, we have atomic clocks, but the constellations are still used by astronomers. All ofthe sky has been divided up into 88 calocated by describing what constellation or area of the sky that it can be foundexample, the Messier objects numbered 9, 10, 12, 14, 19, 62, and 107 are all in the constellation Orion, although the figure outlined by the stars of Orion, do nM Another example is M31. This is the Andromeda galaxy and is found in the constellation, or area of Andromeda, but is not a member of the bright celestial objects that compose the figure of the chained princess awaiting the sea monster. The stars that make up the constellations proper have been labeled by astronomers past and present. Some of the stars simply have numbers or letters, while some have common names. Greek letters are used to denote stars within the constellations, with the brightest star of the constellation, usually, but not always, receiving the Greek letter alpha. Let’s look at the hunter Orion. The alpha star of Orion has a common name, Betelgeuswhich is a red supergiant and is found on Orion’s right shoulder. His left foot is the Bestname, Mintaka. With a magnitude of 7, it can be found as the top star of the three composing Orion’s belt.

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But there are more than stars in the constellation of Orion. In the area that belongOrion, on will find M42, the Orion Nebula and the now famous Horse head Nebula. Although most of the constellations make their appearances on a seasonal basis there ara group of constellations which can be seen every night of observation. For those of us inthe northern hem

s to

e

isphere the are: Ursa Major, Ursa Minor, (Big and Little Bear), assiopeia (Queen of Ethiopia), Ceiphus (King of Ethiopia) and Draco (the Dragon). hese stars are said to be circumpolar, which means to circle the pole. These onstellations circle the north celestial pole, marked by Polaris, never going below the orizon. They move in a counter clockwise direction. Any night, one can see these five

uestions

CTchconstellations. Q : Constellations 1.) What is a constellation? 2.) Why are constellations useful for mapping the sky?

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Coordinate Systems

ow do astronomers find things in the sky? They use a map, sort of. Actually, it is a

function of its temperature and distance, t’s assume for a moment that the ancient folks were correct and that the entire sky is a

for a

circle is

ivided into 60 minutes of arc. For reference, the Sun and Moon are about 0.5 degrees of e

tly overhead having 90 degrees of arc.

he

re standing at the North Pole sampling Mrs. Clauses’ cookies, where would the orth Star or Polaris be located? The star would be directly over your head, straight up.

nce marker is the celestial equator which is an imaginary circle on the hed directly above the Earth’s equator. It is always 90 degrees from the

d

Hcoordinate system. When you are graphing in Algebra class, it is common to say that a point is located at the coordinates (3,4). Astronomers use the same method, but instead of having an x and y axis, they use the celestrial sphere and the Sun’s apparent movement. Let’s look into these ideas. Although we know that a star’s brightness is alegreat sphere circling the Earth. The sphere appears to move from the east to the west.That is, the stars rise in the east and set in the west. We assume that the stars are in asphere, because the Earth is a sphere. Yes, the Earth is the one actually moving, butmoment let’s assume it is the sky that moves. The stars arc, or move across the sky. Because the sky is a sphere, there will be 360 degrees. At any one time you can see 180 degrees of the sky, starting at the easternhorizon and ending at the western horizon. Each of the 360 degrees of thedarc, or 30 minutes of arc. Remember that arc is a term for distance, just like miles. Thbowl of the Big Dipper is 30 degrees for Polaris, the north celestial pole (NCP). If youwere to draw an arc from a point directly to the south of you, one would cover 180 degrees of arc with the point direc The stars rotate around the North and South Celestial Poles. These are points directly above the geographical north and south poles. Imagine that you shoot a line from the geographical poles of the Earth out to the celestial sphere. They would go through tnorth and south celestial poles. If you aNBack in Zuni, is Polaris directly overhead? No. It’s still in the north, but not at 90 degrees. It is located about 35 degrees. The number of degrees above the horizon of the celestial pole is equal to the latitude of the observer. Sailors have known this for 500 years. Another referecelestial sky etccelestial poles. All the stars travel in a path that is parallel to our imaginary equator. On the equator of the Earth, the stars appear to rise in the east, travel directly over head, and set in the west. At the North Pole, the CNP is directly overhead and the stars move alongyour horizon. Let’s go back to Zuni. Assuming you are observing the point directly overhead is callethe zenith. Now, if you find the North point on the horizon and arc a line from it, throughthe zenith and to a South point, this line is called the meridian. Meridian: an imaginary line drawn from due north to due south passing through a point 90 degrees overhead called the zenith. When an object passing through the meridian, it is at its highest

85

altitude, relative to the horizon during the night, with respect to the horizon. The stars will make a path with the highest point reached equal to 90 degrees minus the observers

titude. In Zuni, our latitude is 35 degrees. Therefore, the highest point of the path for

n before setting in the west.

rs in the northern hemisphere, the stars along the celestial equator will be bserved for 12 hours. Those north of the celestial equator, such as Draco, will be seen

or will be seen less than 12

lathe stars will be 55 degrees above the horizon. The celestial equator will arc up to 55 degrees from the southern horizon in Zuni. The stars will still rise in the east and set in the west. They will rise in the east, arc up to a point that is 55 degrees above the southerhorizon For observeofor more than 12 hours and those south of the celestial equathours. Summary: 1.) Meridian goes through due north, zenith, and due south.

es f the

bserver. 4.) A f the obser5.) St

"

refers to how far above the imaginary "celestial equator" an object is (like latitude on the Earth). Try standing in the

st like going "up" in Declination. If you move your arm down to point at some objects on the floor,

at le, and -90 degrees at the South Pole.

2.) Zenith is always directly overhead, 90 degre3.) The altitude of the celestial pole above the horizon is equal to the latitude oo

ltitude of the celestial equator on the meridian is equal to 90 – the latitude over. ars move parallel to the celestial equator.

6.) Stars rise in the east, follow the celestial equator’s arc and set in the west.

Right Ascension & Declination Right Ascension (abbreviated R.A.) and Declination (abbreviated Dec) are a system of coordinates used by astronomers to keep track of where stars and galaxies are in the sky. They are similar to the system of "longitude" and "latitudeused on the Earth.

Declination is measured in degrees, and

middle of a room, and holding your arm out straight in front of you. If you move your arm up to point at a light, or the ceiling, it is ju

you're moving "down" in Declination.

Declination, like latitude, is measured as 0 degrees at the equator, +90 degreesthe North Po

Right Ascension measures the other part of a star's position. It is similar to longitude on the Earth. As you stand in the room, if you spin yourself clockwise to point at a door, then a window, then another door, you are "moving" in Right Ascension.

86

Right Ascension is measured in hours of time. This is convenient for astronombecause, as the Earth rotates, stars appear to rise and set just like the

ers Sun. If you go

out into your backyard in the winter, and lie on your back some night, you might

ancer, scension of 8 hours. This means that if you wait 3 hours

(subtract 5 hours from 8 hours), Cancer will be directly overhead.

st as latitude and longitude uniquely identify the positions of cities on the Earth, Right Ascension and Declination uniquely identify the position of stars and galaxies in the sky.

Source: http://liftoff.msfc.nasa.gov/acadmy/universe.html

Seasonality of Constellations

be able to see the constellation of Orion overhead. Orion has a Right Ascension of 5 hours. Out of the corner of your eye, you might also see the constellation Cwhich is at a Right A

Ju

s

c.

l equinox and autumnal equinox. At the vernal, or spring, equinox around March 1, the Sun crosses the celestial equator and is moving north. Around September 21, it

crosses the celestial equator again this time heading south. The furthest northern point above the celestial equator that the Sun reaches is called the summer solstice; June 21st. In winter the Sun reaches its furthest southern point called the winter solstice, December 21st.

Why do we see certain constellations at certain times of the year? A simple explanation is that as the Earth travels around the Sun, we are exposed at night to different parts of the celestial sphere. All of the constellations are still in place but basically speaking, the sun is between them and us. But let’s once again pretend that we remain stationary and the Sun moves. The sun risein the east, reaches its highest position in the sky at noon, and sets in the west. The sun appears to drift eastward with respect to the stars over a year. The Sun travels through afull 360 degrees of the celestial sphere. This path that the Sun takes is called the ecliptiThe Sun’s path is not parallel to the celestial equator but is actually tilted 23.5 degrees to the equator. The ecliptic and the celestial equator do intersect at two points called the verna2

87

Coordinates

If we observe a star while observing, and say to our friend, “Look at that one”. He might say, “Which one”? One method of locating this star for your friend is by using the ltitude-azimuth system. The altitude of a star is how many degrees above the horizon at it c ed. Use from 0 to 90 for the degrees. Next find the azimuth or degrees

ass. Example: East 45-degrees. This system works well as long as oth ob the same location. If they aren’t, it doesn’t work well at all. One an use ad of the word description for azimuth.

180

tem is

e

ridian. You start a stopwatch. In 1 hour and 30 minutes, Star A now at your local meridian, called transiting or crossing your north-south line, stop the

s his

dian. 18 hours and 36 minutes after the zero ne goes through Aries.

eclination are degrees of latitude measured from the celestial equator. North of the

celestial equator are positive, south objects carrying a negative sign. The NCP has a eclination of 89 degrees 15 arc minutes.

ath an be locatread from a compb servers are inc degrees inste North = 0 East = 90 South = West = 270 The second method of finding the stars is equatorial co-ordinate system. This sysfixed with respect to the stars so the observer’s location is of no importance. Imagine the celestial globe with longitude and latitude lines drawn, just like the Earth. The longitude lines on the celestial sphere are called right ascension (RA). Right ascension is measured not in degrees but hours, minutes, and seconds. The time increases going eastward. Just like longitude is in Greenwich, England. For RA we hava zero line also. The zero line is the point where the Sun crosses the celestial equator in the spring. Close to the constellation of Aries. So this is how it works: Suppose that Aries is on your local meisstopwatch. The time on your stopwatch is Star A’s right ascension. Right ascension iexpressed in a 24-hour format. Example: Star B has a RA of 18 hours 36 minutes. Tmeans that the star will cross our local merili

D

d

88

Right Ascension (Abbreviated as RA, or occasionally as lower-case Greek letter Alpha: α)

Right Ascension is a coordinate on the celestial sphere that is similar to, but not identical to, longitude on the Earth's surface. Right ascension measures the

The other celestial coordinate, Declination

positions of celestial objects in an east-west direction, like longitude, but unlike longitude right ascension is a time-based coordinate.

, is similar to the terrestrial coordinate latitude. A diagram of Right Ascension and Declination appears below:

As the Earth rotates on its axis, the celestial sphere appears to revolve around the Earth, making one complete revolution in one sidereal day (23 hours, 56 minutes, 4 seconds). A sidereal day is thus about 4 minutes shorter than a mean

f

solar day. This time difference between a sidereal and a solar day is the result othe Earth moving 1/365th of the way around the sun during this period.

Think of the celestial sphere as a giant plastic ball with the Earth at the center. The stars are painted on the inside of the plastic ball, along with the lines of the

89

celestial coordinates Right Ascension and Declination. The ball does not move as the Earth turns in the center, but as we here on Earth see it, it looks likball (the celestial sphere) is turning around the Earth. Because the ball is just sitting there, the things that are painte

e the

d onto the ball (stars and coordinate lines) do not move in relation to each other. The whole celestial sphere, stars,

g coordinate lines, and everything, appear to us on Earth to move together, makina complete circle every sidereal day.

Right Ascension is essentially a time measurement. You can think of RA inway: Whenever the point on the celestial sphere that we have set as the "startRight Ascension transits our local meridian, start a stopwatch. When the celestial object of interest (a star, for example) transits our local meridian, stop the stopwatch. The time on the stopwatch is that object's Right Ascension.

this " of

Right Ascension is expressed in units of time on a 24 hour format. A star could have a

ce

RA of 17h 32m , for example. This would mean that the star transited our meridian 17 hours and 32 minutes after the "start" of Right Ascension transited.

Where IS the "start" of Right Ascension? Astronomers needed to pick someplaon the celestial sphere to start timing for Right Ascension. The most obvious place is one of the points on the celestial sphere where the two principle celestial paths, the ecliptic and the celestial equator, cross. There are two such points, one when the ecliptic moves from south of the celestial equator to north of the celestial equator (known as the point of the Vernal Equinox) , and one where the ecliptic moves from north of the celestial equator to south of the celestial(known as the point of the Autumnal Equinox.)

The point chosen was the point of the Vernal Equinox. It is important to understand that the term "Vernal Equinox" can refer to two different things

equator

. Ithis

n situation we mean the point on the celestial sphere where the paths of the

ecliptic and the celestial equator cross near the constellation Aries. (The term "Vernal Equinox" can also mean the moment in time when the sun is actualocated at that point, but this is not the meaning in this context.)

Astronomers use Sidereal T

lly

ime to measure the movement of the celestial sphere. Local sidereal time, that is the sidereal time where we are located, is equal to the right ascension of any celestial object that is transiting our meridian at this particular moment.

nsion. They do NOT

Avoid a common misunderstanding:

Celestial objects (stars, planets, etc...) have a Right Asce have a sidereal time. It does not make sense to say, for example, that the

he Moon's sidereal time is 15h 00m. The Moon does not have a sidereal time. TMoon (or the sun, stars, etc.. does have a Right Ascension.

90

Locations on the Earth have a Sidereal Time. They do NOT have a Right Ascension. It also does not make sense to say, for example, that the Right Ascension of Raleigh is now 21h 00m. Places do not have a Right Ascension.

Look at the diagram below. Let's say that star 2 has a Right Ascension of 06h 00m. The entire celestial sphere slowly moves from left to right over the course of the night, so the positions in relation to the horizon and the meridian of all the stars shown slowly change.

In the diagram, star 2 is just now transiting our local meridian, so our local sidereal time is 06h 00m.

Star 1 has a right ascension of 05h 00m. Star 1 already transited 1 hour ago. When star 1 was on our meridian, our sidereal time then was 05h 00m.

time will beStar 3 has a right ascension of 07h 00m. When star 3 transits our local sidereal

07 00 . Since our local sidereal time is now 06 00 , star 3 will

So you see that the celestial sphere is like a giant clock keeping sidereal time.

Source: http://www.liftoff.msfc.nasa.gov

h m h m

transit in one hour.

91

Sidereal Time

Your sidereal time is the same as the right ascension of the object at your local meridian. or example, let’s say Star 2 is at your local meridian and its RA is 14hours and 13

ime is 14hours and 13minutes. Fminutes. Your sidereal t Questions: Coordinates 1.) What is an equinox? 2.) What is precission and what causes it? 3.) Why do the Sun, moon, and stars all rise in the east and set in the west? 4.) It is 1:30 am Star A is at your meridian. Its sidereal time is 4hours and 15minutes.

ou want to see Star B, which has a sidereal time of 8 hours and 45minutes. When will

ribe star location.

gitude? Give Zuni’s latitude and longitude.

me?

3.) Describe the differences in the apparent movement of the stars in Zuni as well as

5.) Why do we see different constellations at different times of the year? Explain using e Earth’s rotation around the Sun.

YStar B be at your local meridian? 5.) Explain 2 ways to desc 6.) What is circumpolar? 7.) Which constellations are circumpolar for Zuni? 8.) What is latitude and lon 9.) What is sidereal ti 10.) What is zenith? 11.) In Zuni, how would you find the celestial equator? 12.) Describe how you would find the CNP anywhere in the northern hemisphere. 1compared to a location on the equator. 14.) Explain how sailors can determine there coordinates. 1th

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Moon

Motion of the Moon The moon completes one revolution and returns to its starting point on the celestial sphere in 27.3 days, or one sidereal month. The time it takes the moon to go through its phases is about 29.5 days or one synodic month. From the word moon, the word month has evolved. Starting with the new moon which is all but invisible in the sky, the moon rows, or waxes, to a full moon. After the full moon the visibility decreases, or wanes,

gaze e when the moon reflects the least light. The new moon nights are the best for

e oon.

ed fact sheet for the cold hard facts. We will discuss these.

guntil a new moon is created. See the diagram on moon phases. As we will be viewing the stars regularly one should know that the best nights to starare thosstars. But on the full moon nights, we will view the moon. So let’s know about thm See the enclos Surface of the Moon The first astronomers to look at the moon, including Galileo Galilei, saw dark areas that

been named miras or seas. Today there are 19 named “seas” on the

oon, 14 on the lighted side and 5 on the dark side. They range in size from 200km to

tail aters. But due to atmospheric blurring, the best Earth bound telescopes can

solve details 1km across. Craters come from very small to hundreds of kilometers

the

logically speaking, the ighlands are the moon’s crust and the marias are made of mantle material. Radioactive

he moon around 4 billion years.

they thought were oceans. Light areas were also seen that looked like continents The dark flat areas thought to be seas have turned out to be large flat lava flows. But theareas had alreadym1200km in size. Called the highlands, the lighter areas of the moon, are several kilometers above the lava flows. One will also find craters on the moon. Crater is Greek for bowl. Next to the terminator, the line that separates the light and dark sides an observer can see good deof the crreacross. Moon rocks have allowed astronomers to learn about the composition and age ofmoon. Highland rocks contain a lot of aluminum. Explains the light color right? The miria’s basaltic rocks contain iron making it darker. Geohdating puts the age of t Rotation of the Moon The moon has a rotation, it spins; a rotation of 27.3 days which is also equal to the rotation of the moon around the earth. This results in us never seeing the dark side.

hen the spin of one body is precisely equal to its revolution around another body, is ronous orbit.

Wknown as a synch Impacts/Craters Meteoroids have collided with both the moon and the Earth. The moon is littered with craters. We have one in Arizona. At speeds of several kilometers per second meteoroids pack a real punch when they strike the surface. The heat on impact heats the rocks and

93

deforms the rocks. Shock waves pass into the planet. An explosion ensues, pushing rock up and out of the impact point. This material is called the ejecta. As it settles around the formed rim of the crater it forms a layer of material called the ejecta blanket. As a rule othumb, the crater is usually 10 times in diameter relative to the meteoroid that createdcrater. The depth of the crater is also about twice as deep as the me

f the

teoroid’s diameter. ith most of the craters being in the highland areas it is suggested that the lava flow

followed the heaviest of the meteoroid t of the moon.

Wbombardmen

Volcanoes

The moon had volcanoes at one time, but now the volcanoes are geologically dead. Some craters were formed from the collapsing lava flows. One can observe rilles, r lava flows, on the moon’s surface. Dating of the lava rocks indicate that volcanic

activity ceased some 3 billion year

Origin of the Moon

os ago.

Student research project.

Orbit of the Moon

Like most celestial bodies, the moon has an elliptical path. An ellipse is an elongated circle. The amount of elongation is referred to as eccentricity. The eccentricity of theMoon is very small but this eccentricity results in the Moon not being equidistant from the Earth during its orbit. The shortest distan

ce from the Moon to the Earth is called erigee while the longest distance is the apogee. Given time the orbit of the Moon shifts

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3,499 km/hr. If ne is observing the Moon it moves across the sky at a rate of one Moon diameter every

un. When the Sun appears high the sky, it is summer and the Moon will appear low. When the Sun does not rise high

in the sky, it is winter and the Moon will appear high.

pso the perigee and apogee are not constants. The speed of the Moon also changes as Kepler would have predicted. Relative to the Earth the Moon makes one rotation on its axis every 29.5 days. This is the same amounof time that it takes the Moon to revolve around the Earth once. The Moon rotated much faster in the past, but due to the Earth’s gravity, the Moon has slowed. On the equator, the Earth rotates at 1000 miles per hour while the Moon moves at 10 miles per hour. The orbital speed of the Moon is faster than the Earth’s. The average speed of the Moon is 2,287mph (3,683 km/hr). Because of the elliptical nature of the orbit when the Moon is closest to the Earth its velocity is 3,978 km/hr and when furthest away, ohour. During a day, the Moon covers about 13 degrees across the sky. The path that the Sun appears to travel across the sky is called the ecliptic. Traditionally, the signs of the zodiac are located on the ecliptic. Relative to the ecliptic the Moon’s path is tilted 5 degrees. During a revolution around the Earth, the Moon will sweep out a path that is 5 degrees above and below the path of the Sin

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If one thinks of the Sun and Moon each on a plane of travel, there are two locations where the planes intersect. These points are called nodes. The plane of the Moon’s orbit

tates around the Earth. If the nodes fall on the line between the Earth and the Sun, a new or full moon will produce an eclipse the new Moon is between the Earth and the Sun, a new Moon will produce a solar eclipse.

ro. When

Phases

A new moon is the start of a lunar month. It is the dark sphere. Light starts to creep across the surface of the Moon from the right, and when the Moon is half lit, it is called the first quarter. The light proceeds across the Moon with the passage of days until we reach the full Moon. Darkness then starts, again on the right side until the right half is

ark. This is the last quarter Moon. Given another week, the Moon is dark again and we s

rst quarter oon will appear in 7.4 days. The new Moon rises and sets with the Sun, but by day

14.8 when the Moon is now full, the Moon rises at sunset and sets about sunrise. he Moon is 8 to 10 hours ahead of the Sun. By day 22.1 the Moon is in the last quarter,

g, the variation between 2 successive phases should take .38 days, but can vary by as much as 19 hours. This means the change in phases can be

anywhere between 6 and 9 days. are many internet sites that give accurate time for the Moon.

dare back to a new Moon. When the Moon is gaining light, it is called waxing. Waning iwhen the darkness is increasing from the right hand side. During these phases, the Moon takes a predictable time and is in a predictable location, relative to the Moon. If we start with a new Moon, and label that day 0, the fiMseven, is a few hours behind the Sun. At the first quarter, the Moon is above the horizon half in the day, and half during the night and is 8 to 10 hours behind the Sun. On dayTspending half of the day above and below the horizon and precedes the Sun by a fewhours. Although many think of the Moon phases as being constant, the Moon actually has variations in its phase timing. This can be caused by variations of the Moon’s own orbital path or gravity created by the interactions of the Earth, Moon, and Sun. The “official” length of a lunation, the time from one new Moon to the next is 29 days 12 hours and 44 minutes, and 2.8 seconds. But this time can vary from a few minutes to several hours. More confusin7

To our assistance, there

Moonrise and Moonset

Depending on one’s latitude and longitude, the changes in moonrise and moonset vary oa daily basis. As a rule of thumb, however, moonrise and moonset occur about one hour

n

ter each day. During the lunar cycle, there are days when the Moon does not rise or set. This is because the Moon has a 25-hour day. For example: If the Moon set at 11:50pm on Monday night in 25 hours, the next setting time will be 12:40am Wednesday morning.

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Size and Brightness

The apparent size of the Moon, for most Earth observers, is about half of a degree. Sometimes it looks larger. Why? Sometimes the closeness to the horizon allows the Moon to look larger because we compare nearby objects to the Moon. Sometimes theangle of viewing, the differ

ence between seeing the Moon horizontally versus vertically

dds size. The largest difference in size, 10%, is because of the elliptical orbit of the

the source,

the distance. To be exact the intensity ecreases as the square of the distance. Example: If you double the distance the

illumination will be 25% of the original.

aMoon. It is indeed closer. The difference in brightness of the Moon over a period of time can be explained byvarying orbital difference and the law of inverse squares. As light comes from a the intensity decreases, with an increase ind

Halos

When there is moister in the upper atmosphere it is frozen into ice. If the Moon is at a ertain angle the light reflected from the Moon will be refracted at an angle of 22 degrees

If one is at a certain angle to the moon and th atmosphere contains moisture an image of the Moon can be generated that will appear to the Moon. It is called a moondog.

ccreating a halo.

e next

Tilt

As the Moon travels through the night sky it appears to tilt, or change positions relative to

here the crescent might appear. This is caused by the actual orbit of the Moon.

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MOON DATA Amherst Web-Urban MOON Atlas

5/15/01 EARTH-MOON COMPARISON

Diam. mi. Vol. Mass Den. Rotat.

daysRevoldays

Surf.Gravity Spee

Mean Dist. m

. Orbit d

mph i.

EARTH 7,926 63 83 1 1 365.25 1 66,600 --

MOON 2,260 1 1 0.62 27.3 2 2,280 238,000 7.3 0.17

NAMES A Pe k phrodite - F- Greek Hekate - F - Greek rsephone - F - GreeApollo - M - Greek era - F - Greek H Phobe - F - Greek Artemis - F - Greek Is htar - F - Babylon Selene - F - Green Diana - F - Greek Isis - F - Egypt Shing - F - China

D ionysus - M - Greek Juno - F - Rome Somas - M - Greek Ea Tsuki - N - Japan rth-Child - N - 5A Luna - F - Rome Europa - F - Greek Osiris - M - Egypt .

AMERICAN L OFU L MO N NAMES Jan Winter, Old, Wolf, Yule . Jul Summer, Thunder, Buck, Hay Feb Snow, Storm, Hunger . Aug Dog Day, Corn, Grain, Sturgeon Mar Sap, Fish, Crow, Worm . Sep Harvest, Fruit Apr Grass, Pink, Egg, Planters . Oct Hunter's, Blood May Flower, Milk, Hare . Nov Frosty, Beaver Jun Rose, Strawberry, Honey, Hot . Dec C ng Nite, Christmas, Oak old, Lo

MOON DATADiameter: 2,160 miles; Equitorial - 3,476 km; PolaSurface Area: 1,469,00 sq. mi. Mass: 7,340,000,000,000,000,000 kg.; .01227Volume: 5.23 Trillion cubic mDensity: 3.34 Water; .606 Earth Surface Gravity: .166 EartEsacape Velocity: 1.5 mi./sec., 2.38 km./sec.; Earth: 11Orbit Eccentricity: .0549 Distance: Apogee: 252,948 mi.; Perigee: 221,593 mi. Apparent Diameter: Perigee 33' 31"; Apogee: 29' 22" Rotation: Synchronous Orbital Velocity: Mean: 2,287 mph; Max.: 2,429 mpApparent Motion: Approx. 1/2 degree/hr.; 13 degrees/day Mean Sidereal Period: 27d, 7h, 43m = 27.3217 dMean Synodic Period: 29d, 12h, 44m, 2.78s = 29.Mean Orbit Inclination - To Ecliptic: Rotational Axis Inclination - to Orbit: Nodes Revolution: 18y, 10d, 8h, 30m Saros Cycle: 18y, 10d, 7h, 42m Mean Longitudinal Termin1 Degree Longitude at Equator = 18.% Visible from Earth: 58.9 Limb to Limb Distance = 3,391 mi. Surface Temp.: Max.: 118 c.; Min: -153 c.

r - 3,470 km

Earth i.; .0203 Earth

h .2 km./sec.; 21.3% Earth

h; Min: 2,153 pmh

ays 5306 days

5d 8' 43" 1d 0' 30"s

ator Motion: 11.49 degrees/day = 216.47 mi. at Eq. 84 mi.

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Albedo: .073 Apparent Magnitude: Full: -12.6; Quarter: -10.2 Coordinate System: 0 in Sinus Medii Shape: Triaxial Ellipsoid, Flattened at Poles, Bulge ler Bulge opposite Earth

ORBIT DATA

27.32158 days us Month,

.2122 days

from Earth to Moon 0 km. below Earth Surface

erage Distance (Apogee) km. below Earth Surface

ts to Sun Sun

, 10m) about 3 degrees per Orbit.

Ecliptic riod

m Ecliptic ,793.5 days (18.6 yrs.)

es (W., back) .053 degrees per day

9 degrees per year s (New to Full) have Eclipse,

ngular Distance of Earth & Sun, measured form Moon s phase angle)

Synchronous Rotation

.) Limb exposed b exposed

iurnal - Measured from position on Earth & Earth Rotation E. to W. hysical - Slight Rotational Irregularity from Triaxial Ellipsoidal Shape

towards Earth, SmalLagrange Points: 5

SIDEREAL MONTH - Time to same R.A. Position; 27.32166 days; Precession 3.76", Increases 7 sec./yr. TROPICAL MONTH - Sidereal Month minus Precession; SYNODIC MONTH - New-New, Full-Full Phase; Most conspicuo360 degrees times Sidereal Month divided by Sidereal Year ANOMALISTIC MONTH - Perigee to Perigee; 27.55455 days DRACONIC MONTH - Node to Node; 27BARYCENTER - Earth-Moon Mass Center; Revolves around Sun; Earth Revolves around Barycenter 1/month Moves 1,196 km./hr. in Earth Mantle; 1/81.3 distance 4,727 km. from Earth Center; 1,65Earth Center can be 456 km above/below Ecliptic Barycenter Orbit defines Ecliptic ECCENTRICITY - .054900 from Barycenter; Varies 5.49% from AvBarycenter varies from 1,900 (Perigee) to 1,400Ellipcity varies - stretched (greater) when Apsides Axis poinmore circular (less) when at right angle toPerigee closer at Full & New, further at 1st & Last Quarter Apogee distance varies less than Perigee Asides Axis Precesses E. (forward) in 2,236.2 days (18yApsides: Line through Perigee-Apogee Apogee about 252,948 mi.; Perigee about 221,593 mi. INCLINATION - Varies about 5 degrees 8' 43" (5.145 degrees) from Ecliptic Moon can be 37,000 km. (5.29 degrees) above/below Max. 29 degrees N. or S. Declination, Varies 59' (.15 degrees) in 173 day peMoon Can Occult any Star 5.5 degrees froNutation Period: Recession Cycle of Inclination; 6Recesses W. (back) .053 degrees per day Node: Point where Moon's Center crosses Ecliptic Nodal Period: 2.6 hrs less than Sidereal, Node RecessNode Alignment: Axis of Nodes points to Sun each 173.3 days Line of Nodes Recesses W about 1Eclipse Season: about 1 or 6 SyzygyUsually 4 Eclipses/yr., max of 7 PHASE - SYZYGY = New to Full Waxing = Growing; Waning = Shrinking; Crescent = Less than 1/2 Lit; Gibbous = more than 1/2 Lit Elongation = Angular Distance of Moon from Sun Phase Angle = AIlluminated Fraction = % of Lit Moon facing Earth = 1/2(1+coLIBRATION Longitude - from Elliptical Orbit & about 6 degrees 17', max. 7 degrees 54' Rotation nearly constant so at - 1/2 Time from Perigee to Apogee (> 1/2 Orbital Distance) Right (E1/2 Time from Apogee to Perigee (< 1/2 Orbital Distance) Left (W.) LimLatitude - Rotational Axis inclined 6 degrees 50' to Orbital Plane DP

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Source: http://www.amastro.org/at/mo/mod.html

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Questions: Moon 1.) Why can’t one observe the stars well on a full Moon night? 2.) Why does the Moon rise 50 minutes later than the day before? 3.) If the Moon revolves, why do we never see the dark side? Please draw a diagram. 4.) What causes a halo around the Moon? 5.) Give some common names for the full moon. 6.) What is a maria and what is it made of? 7.) What is basalt? 8.) Describe bow an eclipse happens. 9.) What are the parts to a crater and how did they get to be what they are? 10.) What is a synodic month? 11.) What would be the length of the synodic month of the Moon’s sidereal orbital period were: One week (7 days, solar) 12.) Why doesn’t the Moon have an atmosphere? 13.) How do we know that the highlands are older than the marias?

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Fundamentals

Kepler’s Laws 1.) The orbital paths of the planets are elliptical, with the Sun at one focus. 2.) An imaginary line connection the Sun to any planet sweeps out equal areas of the ellipse in equal intervals of time. 3.) The square of a planet’s orbital period is proportional to the cube of its semi-major axis. P² (Earth’s years) = a³ (in A.U.) Where: P = Orbital Period a = Orbital Semi-Major Axis Length Newton’s Laws of Motion 1.) An object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an unbalanced force. 2.) Force is a function of an objects mass and acceleration. F = ma 3.) For every action, there is an equal and opposite reaction. Gravity Every particle of matter in the universe attracts every other particle with a force directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them. Gravitational Force ∞ mass of Object 1 x mass of Object 2/distance² OR F = G m1 m2 r² Where: G = gravitational constant 6.67 x 10^-11 N m²/kg² Escape Velocity V escape = √2GM/r Where: G = gravitational constant M = Mass of planet r = radius of the planet

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Copernican Principles 1.) The celestial spheres do not have just one common center. 2.) The center of the Earth is not the center of the universe but is instead only the center of gravity and of the lunar orbit. 3.) All spheres revolve around the Sun. 4.) The stars are further away than the Sun. 5.) The apparent motion of the stars results from the Earth’s rotation. 6.) The Sun’s apparent daily and yearly motion are due to the motions of the Earth. 7.) The apparent retrograde motion of the planets is due to the motion of the Earth. Momentum The amount of energy in a moving body. Linear p = mv Where: p = momentum m = mass of the object v = velocity of the object Angular: The amount of energy in a rotating body L = mvr Where: L = angular momentum m = mass of the body v = velocity of the body r = radius of the body * Momentum is conserved.

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Fundamentals

1.) An asteroid has a perihelion of 2AU and an aphelion of 4.0AU. Calculate its orbital semi-major axis. 2.) Why is the escape velocity independent of an objects mass? 3.) Halley’s Comet has a perihelion of distance of 6.0AU and an orbital period of 76 years. Find the aphelion from the Sun. 4.) The acceleration due to gravity at the Earth’s surface is 9.8m/s². What is the gravitational acceleration at altitudes of: a.) 100km b.) 1000km c.) 10,000km Assume Earth’s radius to be 6400km. 5.) Use Newton’s Law of gravity to calculate the force of gravity between you and the Earth. Convert your answer to pounds with 4.45N = 1 pound 6.) The Moon’s mass is 7.4 x 10^22kg and its radius is 1700km. Calculate the escape velocity.

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Glossary

Topic: Galaxies

Accretion Disk

A relatively flat, rapidly rotating disk of gas surrounding a black hole, a newborn star, or any massive object that attracts and swallows matter. Accretion disks around stars are expected to contain dust particles and may show evidence of active planet formation. Beta Pictoris is an example of a star known to have an accretion disk.

Active Galactic Nucleus (AGN)

A very bright, compact region found at the center of certain galaxies. The brightness of an active galactic nucleus is thought to come from an accretion disk around a supermassive black hole. The black hole devours matter from the accretion disk, and this infall of matter provides the firepower for quasars, the most luminous type of active galactic nucleus.

Active Galaxy

A galaxy possessing an active galactic nucleus at its center.

Afterglow

The fading fireball of a gamma-ray burst — a sudden burst of gamma rays from deep space — that is observable in less energetic wavelengths, such as X-ray, optical, and radio. After an initial explosion, an expanding gamma-ray burst slows and sweeps up surrounding material, generating the afterglow, which is visible for several weeks or months. The afterglow is usually extremely faint, making it difficult to locate and study.

Barred Spiral Galaxy

A galaxy with a “bar” of stars and interstellar matter, such as dust and gas, slicing across its center. The Milky Way is thought to be a barred spiral galaxy.

Black Hole

A region of space containing a huge amount of mass compacted into an extremely small volume. A black hole’s gravitational influence is so strong that nothing, not even light, can escape its grasp. Swirling

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disks of material — called accretion disks — may surround black holes, and jets of matter may arise from their vicinity.

Bulge

The spherical structure at the center of a spiral galaxy that is made up primarily of old stars, gas, and dust. The Milky Way’s bulge is roughly 15,000 light-years across.

Colliding Galaxies

A galactic “car wreck” in which two galaxies pass close enough to gravitationally disrupt each other’s shape. The collision rips streamers of stars from the galaxies, fuels an explosion of star birth, and can ultimately result in both galaxies merging into one.

Dark Matter

Matter that is too dim to be detected by telescopes. Astronomers infer its existence by measuring its gravitational influence. Dark matter makes up most of the total mass of the universe.

Dwarf Galaxy

A relatively small galaxy. The Large and Small Magellanic Clouds, visible in the Southern Hemisphere, are two dwarf irregular galaxies that are neighbors of the Milky Way.

Elliptical Galaxy

A galaxy that appears spherical or football-shaped. Elliptical galaxies are comprised mostly of old stars and contain very little dust and “cool” gas that can form stars.

Galactic Center

The central hub or nucleus of a galaxy. The Milky Way’s galactic center is about 28,000 light-years from Earth.

Galactic Disk

A flattened disk of gas and young stars in a galaxy. Some galactic disks have material concentrated in spiral arms (as in a spiral galaxy) or bars (as in barred spirals).

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Galactic Halo

Spherical regions around spiral galaxies that contain dim stars and globular clusters. The radius of the halo surrounding the Milky Way extends some 50,000 light-years from the galactic center.

Galactic Nucleus

The central concentration of matter (stars, gas, dust, and perhaps a black hole) in a galaxy, typically spanning no more than a few light-years in diameter.

Galactic Plane

The imaginary projection of the Milky Way’s disk on the sky. Most of the galaxy’s stars and interstellar matter reside in this disk. Objects in the galaxy are often referred to as being above, below, or in the galactic plane.

Galaxy

A collection of stars, gas, and dust bound together by gravity. The smallest galaxies may contain only a few hundred thousand stars, while the largest galaxies have thousands of billions of stars. The Milky Way galaxy contains our solar system. Galaxies are classified or grouped by their shape. Round or oval galaxies are elliptical galaxies and those showing a pinwheel structure are spiral galaxies. All others are called irregular because they do not resemble elliptical or spiral galaxies.

Galaxy Cluster

A collection of dozens to thousands of galaxies bound together by gravity.

Galaxy Evolution

The study of the birth of galaxies and how they change and develop over time.

Galaxy Supercluster

A vast collection of galaxy clusters that may contain tens of thousands of galaxies spanning over a hundred million light-years of space. Galaxy superclusters are the largest structures in the universe.

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Globular Cluster

A collection of hundreds of thousands of old stars held together by gravity. Globular clusters are usually spherically shaped and are often found in the halos of galaxies. Each star belonging to a cluster revolves around the cluster’s common center of mass.

Gravitational Clustering

The process by which a large-scale structure grows as its gravity attracts smaller building blocks. Astronomers believe that all the large-scale structures (such as galaxies, galaxy clusters, and galaxy superclusters) that we see in the universe today formed through gravitational clustering.

Gravitational Lens

A massive object that magnifies or distorts the light of objects lying behind it. For example, the powerful gravitational field of a massive cluster of galaxies can bend the light rays from more distant galaxies, just as a camera lens bends light to form a picture.

Group of Galaxies

A small collection of galaxies bound together by gravity. The number of galaxies in a group can range from a few to dozens. The Milky Way is a member of the Local Group, a collection of more than 30 galaxies.

HDF-N

Hubble Deep Field North (HDF-N) is a tiny region of the northern sky near the Big Dipper toward which the Hubble Space Telescope was pointed for ten straight days in 1995. Because this observation was designed to detect very faint light from the most distant galaxies Hubble can observe, the field contains few bright celestial objects. Seemingly devoid of light, this small area provided a “keyhole” view of the universe’s past, reaching across space and time to see infant galaxies. By probing these remote regions of space, astronomers are gaining more information on galaxy development.

HDF-S

Hubble Deep Field South (HDF-S) is a tiny region of the southern sky near the Southern Cross toward which the Hubble Space Telescope was pointed for ten straight days in 1998. Because this observation was designed to detect very faint light from the most

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distant galaxies Hubble can observe, the field contains few bright celestial objects. Seemingly devoid of light, this small area provided a “keyhole” view of the universe’s past, reaching across space and time to see infant galaxies. By probing these remote regions of space, astronomers are gaining more information on galaxy development.

Host Galaxy

A galaxy in which a cosmic phenomenon, such as a supernova explosion or a gamma-ray burst, has occurred.

Interstellar Dust

Small particles of solid matter, similar to smoke, in the space between stars.

Interstellar Medium (ISM)

The sparse gas and dust located between the stars of a galaxy.

Interstellar Space

The dark regions of space located between the stars.

Irregular Galaxy

A galaxy that appears disorganized and disordered, without a distinct spiral or elliptical shape. Irregular galaxies are usually rich in interstellar matter, such as dust and gas. The Large and Small Magellanic Clouds are examples of nearby irregular galaxies.

Local Group

A small cluster of more than 30 galaxies, including the Andromeda galaxy, the Magellanic Clouds, and the Milky Way galaxy.

Magellanic Clouds

The Magellanic Clouds are two dwarf irregular galaxies. Known as the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), the galaxies are in the Local Group. The closer LMC is 168,000 light-years from Earth. Both galaxies can be observed with the naked eye in the southern night sky.

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Milky Way Galaxy

The Milky Way, a spiral galaxy, is the home of Earth. The Milky Way contains more than 100 billion stars and has a diameter of 100,000 light-years.

Open Cluster

Also known as a galactic cluster, an open cluster consists of numerous young stars that formed at the same time within a large cloud of interstellar dust and gas. Open clusters are located in the spiral arms or the disks of galaxies. The Pleiades is an example of an open cluster.

Protogalaxy

Matter that is beginning to come together to form a galaxy. It is the precursor of a present-day galaxy and is sometimes called a “baby galaxy.”

Quasar

The brightest type of active galactic nucleus, believed to be powered by a supermassive black hole. The word “quasar” is derived from quasi-stellar radio source, because this type of object was first identified as a kind of radio source. Quasars also are called quasi-stellar objects (QSOs). Thousands of quasars have been observed, all at extreme distances from our galaxy.

Seyfert Galaxy

A galaxy characterized by a moderately bright, compact active galactic nucleus, presumably powered by a black hole.

Singularity

A black hole’s center, where the matter is thought to be infinitely dense, the volume is infinitely small, and the force of gravity is infinitely large.

Spiral Arms

A pinwheel structure, composed of dust, gas, and young stars, that winds its way out from the core of a normal spiral galaxy and from the ends of the bar in a barred spiral galaxy.

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Spiral Galaxy

A spiral-shaped system of stars, dust, and gas clouds. A typical spiral galaxy has a spherical central bulge of older stars surrounded by a flattened galactic disk that contains a spiral pattern of young, hot stars, as well as interstellar matter.

Starburst Galaxy

A galaxy undergoing an extremely high rate of star formation. Starburst galaxies contain massive, deeply embedded stars that are among the youngest stars observed.

Stellar Black Hole

A black hole formed from the death of a massive star during a supernova explosion. A stellar black hole, much like a supermassive black hole, feeds off of nearby material — in this case, the dead star. As it gains mass, its gravitational field increases.

Supermassive Black Hole

A black hole possessing as much mass as a million or a billion stars. Supermassive black holes reside in the centers of galaxies and are the engines that power active galactic nuclei and quasars.

Source: http://hubblesite.org/reference_desk/glossary/galaxies.shtml

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Useful Constants Physical Constants

Gravitational constant G = 6.672(4)*10^-8 cm^3 g^-1 sec^-2 Velocity of light (vacuum) c = 2.99792458*10^10 cm s^-1 (by definition !) Planck's constant h = 6.62618(4)*10^-27 erg s

hbar = 1.054589(6)*10^-27 erg s Boltzmann's constant k_B = 1.038066(4)*10^-16 erg K^{-1} Electron charge e = 4.80324(1)*10^-10 esu

e = 1.602189(5)*10^-19 Coulomb Proton mass m_p = 1.6726949(9)*10^-24 g Electron mass m_e = 9.10953(5)*10^-28 g Stefan-Boltzmann constant sigma = pi^2 k_B^4/(60 hbar^3 c^2)

sigma = 5.6703(7)*10^-5 erg s^-1 cm^-2 K^-4 Thomson cross section sigma_T = 8 pi e^4/(3 m_e^2 c^4)

sigma_T = 6.65245(6)*10^-25 cm^2

Astronomical Constants

Astronomical Unit 1 AU = 1.49597892(1)*10^13 cm

Light-Year 1 ly = 9.4608953536(1)*10^17 cm

Parsec 1 pc = 648,000/pi AU (by definition) 1 pc = 3.08567802(2)*10^18 cm 1 pc = 3.26150740(2) ly

(Siderial) Year (1900) 1 yr = 3.1558149984*10^7 s

Solar Mass M_sun = 1.989(2)*10^33 g G * M_sun = 1.32712497(1)*10^26 cm^3 s^-2

Solar radius R_sun = 6.9599(7)*10^10 cm

Bolometric Solar Luminosity L_sun = 3.826(8)*10^33 erg s^-1

Escape velocity from Sun v_* = 617.5 km s^-1

Absolute Solar Magnitude M_v = +4.83

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M_B = +5.48

Earth Mass M_earth = 5.976(4)=10^27 g

Hubble constant H0 = 60..75 km s^-1 Mpc^-1 H0 = 18..23 km s^-1 Mly^-1 H0 = 1.9..2.4 *10^-18 s^-1

Hubble Time H0^-1 = 4.1..5.2*10^17 s H0^-1 = 13.0..16.3*10^9 yr

Values in parentheses give inacuracy in preceding digit.

Useful approximate relations:

1 km/s ~ 1 pc per million y (1.023) M_sun/L_sun ~ 0.5 in cgs units (0.52) 1 radian = 206,265" , 1 pc = 206,265 AU (648,000/pi)

References

• James Binney and Scott Tremaine, Galactic Dynamics. 1987 Princeton UP, ISBN 0-691-08445-9. Appendix 1.A.

• Physical Constants from Astrophysical Formulae by Kenneth R. Lang.

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Greek alphabet

If the table below does not contain Greek characters, then you are probably using Netscape 6.1;

earlier versions of Netscape or any version of Internet Explorer will display the proper characters.

The Greek Alphabet (lower case)

alpha α ι iota ρ rho

β beta κ kappa σ sigma

γ gamma λ lambda τ tau

δ delta μ mu υ upsilon

ε epsilon ν nu ϕ phi

ζ zeta ξ xi χ chi

η eta ο omicron ψ psi

ϑ theta π pi ω omega

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Constellations

The tradition of creating shapes from patterns of stars has been around for as long as mankind. I have included stories and folklore from many different sources.

Constellations have been documented in many different forms, such as pottery, coins, and other items dating back to 4000 B.C. The Greek poet Aratus of Soli gave a verse description of 44 constellations in his Phaenomena. The Greek astronomer and mathematician Ptolemy, in his Almagest, described 48 constellations, of which 47 are known today by the same name.

At the end of the 16th century the first European explorers of the South Seas mapped the southern sky, which was largely unknown to the inhabitants of the northern hemisphere. New constellations were added by a Dutch navigator, Pieter Dirckz Keyser, who participated in the exploration of the East Indies in 1595. Subsequently, other southern constellations were added by the German astronomer Johann Bayer (1572-1625), who published the first extensive star atlas in the Western world, the Uranometria; by Polish astronomer Johannes Hevelius (1611-1687); and by the French astronomer Nicolas-Louis de Lacaille (1713-62).

Although many constellations had been mapped out, it wasn't until 1930 that definitive boundaries were fixed by the International Astronomical Union.

Name Abbreviation Pronunciation

Andromeda AND an DROM a duh

Size (Degrees ²) Meaning Classification 722 chained lady person

Andromeda was the daughter of Cassiopeia the beautiful Aethiopian queen of the city of Joppa in Phoenicia. Cepheus, the king, was her father. Andromeda’s mother, Cassiopeia, was boastful about her natural beauty and especially the beauty of her daughter Andromeda. One day after boasting that she and Andromeda were more beautiful than the sea nymphs, Poseidon, god of the sea, decided to punish the queen for her vanity. He sent a terrible sea monster, Cetus, to destroy Phoenicia. King Cepheus quickly consulted the Oracle at Ammon, where he was advised that Poseidon could only be appeased if the sacrificed their daughter Andromeda to Cetus. So, they chained Andromeda to a rock on a tiny island offshore to await her death. The hero Perseus, returning from killing the Gorgon Medusa saw Andromeda’s plight, slew Cetus and rescued Andromeda. The constellations of Cassiopeia, Cepheus, Andromeda, Perseus, Pegasus and Cetus, represent characters that appear in the story of Perseus

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Messier Objects in Andromeda: M-31 M-32 M-110

Name Abbreviation Pronunciation

Antlia ANT ANT lee uh

Size (Degrees ²) Meaning Classification 239 air pump object

This constellation of the southern hemisphere was named in modern times; it contains no bright stars and none with a proper name. Although visible from the mid-northern hemisphere near the horizon due south of Leo when that constellation culminates, Antlia’s stars are so faint that stargazers in antiquity didn’t bother to name them. From 1750 to 1754, French astronomer Nicolas-Louis de Lacaille (1713-1762) compiled a catalog of more than 10,000 stars visible from the Cape of Good Hope; to facilitate his task he mapped out some new constellations. Among these was Antlia Pneumatica, the Air Pump, which he named in honor of the 17th century British chemist Robert Boyle, who invented the compressed-air pump. In 1930 when the International Astronomical Union codified the constellations, the name was shortened to Antlia.

Name Abbreviation Pronunciation

Apus APS AY pus

Size (Degrees ²) Meaning Classification 206 bird of paradise animal

This constellation lies less that 20 degrees from the south celestial pole and is therefore invisible from most northern latitudes. If first appeared on star maps in 1603, in Johann Bayer’s famous Uranometria. Bayer gives credit for its discovery to several explorers of the Southern Hemisphere, including Amerigo Vespucci.

Name Abbreviation Pronunciation

Aquarius AQR uh QWAR ee us

Size (Degrees ²) Meaning Classification 980 water bearer person

Aquarius, one of the most ancient constellations in the sky, has been known under various names over the ages. It is located in a region of the sky that was known thousands of years ago as "the water" or "the sea". and is near other watery figures as Cetus, Pisces, Capricornus, Delphinus, Piscis Austrinus, and Eridanus. The constellation portrays a man or boy spilling water from an urn, although it is difficult to see any figure in the straggling assortment of mostly faint stars visible in the

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southern sky in the autumn. Aquarius was at times identified with Zeus pouring the waters of life down from the heavens; sometimes the celestial river Eridanus is shown to have its source at the urn.

Later Aquarius came to be identified with Ganymede, a beautiful young shepherd who was abducted by Zeus and taken to Mount Olympus to be the cup bearer to the gods. (The constellation Crater, is sometimes identified as Ganymede’s cup.) The constellation Aquarius was named by the Sumerians after their god of heaven An, who pours the waters of immortality upon the earth. Aquarius also figures in a very old Sumerian myth of a global deluge, thought to be the story that gave rise to the biblical story of the Flood. The name of several stars in Aquarius refer to good luck, probably because in ancient times the constellation’s solstitial rising occurred at the start of the rainy season and seemed to bring relief to the arid climes of the Middle East. Aquarius is the first constellation of both the Chinese and the Indian calendars and is again associated with water.

Messier Objects in Aquarius: M-2 M-72 M-73

Name Abbreviation Pronunciation

Aquila AQL AK wil uh

Size (Degrees ²) Meaning Classification 652 eagle animal

The constellation Aquila, identified as a bird since about 1200 B.C., is said to be the eagle that held the thunderbolts of Zeus, king of the gods, until he needed them. Aquila was sometimes sent on other errands by Zeus: It was Aquila that kidnapped the young Ganymede as he tended his flock on the slopes of Mount Ida and brought him to Olympus to serve as cup bearer to the gods. The three brightest stars of Aquila figure in Indian mythology as footprints of the god Vishnu. In Japanese, Korean, and Chinese mythology the brightest star of Aquila, Altair, is identified as the herdsman, Ch’ien Niu, keeper of the royal herds. He fell in love with the maiden Chih Nu (called Tanabata in Japan), whose father was the sun king, the star we call Vega. Ch’ien Niu and Chih Nu married, but they were so in love that they neglected their duties, and the sun king banished them to spend their lives on opposite sides of the celestial river, the Milky Way. The are said to meet once a year, on the seventh day of the seventh month, when magpies stretch their wings across the river for one night - but only if the weather is clear. If it rains even the celestial birds cannot span the flood.

Name Abbreviation Pronunciation

Ara ARA AY ruh

Size (Degrees ²) Meaning Classification 237 alter object

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The group of faint stars we now call Ara was once considered part of the constellations Centaurus and Lupus; it became separated from them when the modern constellation Norma was interposed. Its original Latin name, Ara Centauri, reveals this connection: Ara is the altar of the centaur Chiron. Half man and half horse, Chiron was believed to be the wisest creature on Earth. It was he who first brought order to the sky by showing mortals how to draw lines between the stars to form the constellations. Ara was also sometimes called the Altar of Dionysus. It appears on some old star maps as a tripod censer or brazier. Its H-like shape does not much resemble an altar. Early depictions portray it upright, with smoke from the altar rising northward into the Milky Way.

Name Abbreviation Pronunciation

Aries ARI AIR eez

Size (Degrees ²) Meaning Classification 441 ram animal

The Egyptians of the New Kingdom (which began in the 16th century B.C.) identified this group of stars as a ram, an animal the associated with their principal god, Amon Ra. For the ancient Greeks, the group of stars represented the ram from which the Golden Fleece was taken. According to one myth, King Athamas of Thessaly had two children, Phrixus and Helle, by his first wife, who died when they were still very young. Athamas remarried, but, unbeknownst to him, his second wife hated the children and was cruel to them. The god Hermes took pity on the children and fashioned a magical ram, with wool of gold, to carry them to a land of safety. When the ram appeared to the children, the leapt on its back, and the ram flew into the sky, heading east. Helle lost her grip on the ram and fell into the body of water that separates Europe from Asia, which the Greeks called the Hellespont ("sea of Helle"; now known as the Dardanelles). Phrixus, though, was carried safely to Colchis, on the southeastern shore of the Black Sea, where he found refuge with king Aeetes. He sacrificed the ram and Aeetes hung it in a grove guarded by a sleepless dragon. There the Golden Fleece remained until it was stolen by Jason and the Argonauts.

Name Abbreviation Pronunciation

Auriga AUR aw RYE guh

Size (Degrees ²) Meaning Classification 657 charioteer person

Auriga was among the earliest constellations to be named, but its origins are not known. It is seen as a charioteer, usually identified with either Hephaestus (the Roman god Vulcan), or his son, Erechtheus, both of whom were lame. Each of these figures was credited by the Greeks with inventing the chariot to aid in his transportation. This group of stars has also long been associated with goat herds. In what may be a

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shoulder, represented by the very bright star Capella, and with two or three kids on his arm. Capella was identified by the Greeks with Amalthea, the goat that nursed the infant Zeus. While playing with the animal the baby god broke off one of its horns, which he later imbued with the magical capability of dispensing great quantities of food and drink to whoever desired them - the cornucopia. In India, Capella was considered the ’heart of Brahma’, while natives of Peru called it Colca and also associated it with herders of flocks.

Messier Objects in Auriga: M-36 M-37 M-38

Name Abbreviation Pronunciation

Bootes BOO bow OH teez

Size (Degrees ²) Meaning Classification 907 herdsman person

One legend says the Bootes, whose name comes from the Greek word for "ox-driver" or "herdsman", was the son of Demeter (Roman: Ceres), the goddess of agriculture. The constellation of Bootes was once also know as Arcturus. Bootes is credited with inventing the plow and was placed in the sky to honor his invention, of such immense importance to civilization. In another myth, Bootes was the son of Zeus and Callisto. Callisto, transformed into a bear by Zeus’s jealous wife, Hera, was in danger if being killed by her son Bootes, who was out hunting, until she was rescued by Zeus, who took her into the heavens. There Callisto became the constellation of Ursa Major, the Great Bear.

Name Abbreviation Pronunciation

Caelum CAE SEE lum

Size (Degrees ²) Meaning Classification 125 chisel object

Caelum was named by the 18th century French astronomer Nicolas-Louis de Lacaille.

Name Abbreviation Pronunciation

Camelopardalis CAM cuh MEL oh PAR duh lus

Size (Degrees ²) Meaning Classification 757 giraffe animal

Camelopardalis was named by German astronomer Jakob Bartsch in 1624.

Name Abbreviation Pronunciation

Cancer CNC KAN sir

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Size (Degrees ²) Meaning Classification 506 crab animal

In Greco-Roman mythology Cancer was a crab sent by Hera to distract Hercules while he was fighting Hydra. Cancer nipped Hercules, who then stepped on Cancer and killed it. Hera placed the crab in the sky, but because it had failed in its task, Hera neglected to give Cancer any bright stars to mark the constellation.

Messier Objects in Cancer: M-44 M-67

Name Abbreviation Pronunciation

Canes Venatici CVN KAY neez VEN at ih see

Size (Degrees ²) Meaning Classification 465 hunting dogs animal

Often shown as a pair of greyhounds, these are the hunting dogs of Bootes. They are in leashed of pursuit of the bears Ursa Major and Ursa Minor .

Messier Objects in Canes Venatici: M-3 M-51 M-63 M-94 M-106

Name Abbreviation Pronunciation

Canis Major CMA KAY niss MAY jor

Size (Degrees ²) Meaning Classification 380 greater dog animal

One of the hunter Orion’s hunting dogs. (Canis Minor being the other.)

Messier Objects in Canis Major: M-41

Name Abbreviation Pronunciation

Canis Minor CMI KAY niss MY nor

Size (Degrees ²) Meaning Classification 182 lesser dog animal

Canis Minor, the little dog, is the companion of Canis Major and is the other hound of Orion. Some say that Canis Minor is not a hunting dog but merely a pet faithfully following Orion around the sky.

Name Abbreviation Pronunciation

Capricornus CAP CAP rih COR nus

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Size (Degrees ²) Meaning Classification 414 sea goat animal

Capricornus is one of the oldest constellations in the sky. Depiction’s of a goat, or of a goat-fish, have been found on Babylonian tablets around 3,000 years old. According to some ancient myths, Capricornus was the gate of the Gods, the portal in the sky through which the souls of mortals passed after they died. Capricornus is also identified with the lusty god Pan, who was known to be flighty. The story goes that Pan and some other gods were picnicking along the banks of the Nile. During their feast the monster Typhon came upon them. To escape Typhon the gods turned themselves into animals and fled. Pan panicked and was unable to decide what to become. Finally, he leapt feet first into the river. Just as half of him disappeared into the water, that half became a fish. The half that was above the water became a goat.

Messier Objects in Capricornus: M-30

Name Abbreviation Pronunciation

Carina CAR cuh RYE nuh

Size (Degrees ²) Meaning Classification 494 keel object

Carina was once part of the group of stars known as Argo Navis, the ship that carried Jason and the Argonauts on their quest for the Golden Fleece.

Name Abbreviation Pronunciation

Cassiopeia CAS CAS ee oh PEE ah

Size (Degrees ²) Meaning Classification 598 queen person

Cassiopeia was the beautiful Aethiopian queen of the city of Joppa in Phoenicia. Cepheus was her king husband. Cassiopeia was boastful about her natural beauty and especially the beauty of their daughter Andromeda. One day after boasting that she and Andromeda were more beautiful than the sea nymphs, Poseidon, god of the sea, decided to punish the queen for her vanity. He sent a terrible sea monster, Cetus, to destroy Phoenicia. King Cepheus quickly consulted the Oracle at Ammon, where he was advised that Poseidon could only be appeased if the sacrificed their daughter Andromeda to Cetus. So, the chained Andromeda to a rock on a tiny island offshore to await her death. The hero Perseus, returning from killing the Gorgon Medusa saw Andromeda’s plight, slew Cetus and rescued Andromeda. The constellations of Cassiopeia, Cepheus, Andromeda, Perseus, Pegasus and Cetus, represent characters that appear in the story of Perseus.

Messier Objects in Cassiopeia: M-52 M-103

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Name Abbreviation Pronunciation

Centaurus CEN sen TOR us

Size (Degrees ²) Meaning Classification 1060 centaur person

Centaurus is one of two centaurs in the sky, the other being Sagittarius. Centaurus is said to be Chiron, the smartest and the wisest of his race, wiser even than the gods. He was skilled in the arts, hunting, and medicine. He was the tutor of such illustrious humans as Jason, Achilles, Hercules, and Asclepius. According to early Greek myths, it was Chiron who first fashioned the constellations and showed mankind how to read the sky. He placed a picture of himself in the sky to guide the Argonauts on their quest for the Golden Fleece. Chiron, created immortal, was accidentally wounded by Hercules with an arrow tipped in the venomous blood of the many headed serpent Hydra. Although he could not die, he was in excruciating pain. He pleaded with the gods to release him from the torture of immortality and offered a bargain: his own life for the release of Prometheus, the Titan who had stolen fire from the gods and given it to mankind. Finally, Zeus agreed and let Chiron die. Zeus wanted to place Chiron in the heavens to commemorate him, but by this time the whole northern sky was filled, so Chiron became Centaurus, far to the south and rarely seen in the northern sky.

Name Abbreviation Pronunciation

Cepheus CEP SEE fee us

Size (Degrees ²) Meaning Classification 588 king person

Cepheus was the king of an ancient land called Aethiopia. See the story of Andromeda.

Name Abbreviation Pronunciation

Cetus CET SEE tus

Size (Degrees ²) Meaning Classification 1231 whale animal

The ancient Mesopotamian civilizations identified these stars with Tiamat, the cosmic dragon slain by the hero Marduk. In classical mythology Cetus is the sea monster that threatened Andromeda. In modern times Cetus is portrayed as a whale.

Messier Objects in Cetus: M-77

Name Abbreviation Pronunciation

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Chamaeleon CHA shuh MAY lee on

Size (Degrees ²) Meaning Classification 132 chameleon animal

Chamaeleon was originally sketched out in 1603 by Johann Bayer.

Name Abbreviation Pronunciation

Circinus CIR SIR sin us

Size (Degrees ²) Meaning Classification 93 drawing compass object

Circinus was designated by the 18th century French astronomy Nicolas-Louis de Lacaille.

Name Abbreviation Pronunciation

Columba COL co LUM buh

Size (Degrees ²) Meaning Classification 270 dove animal

Columba is a modern constellation that began appearing in publications in 1679.

Name Abbreviation Pronunciation

Coma Berenices COM CO muh BER uh NI ceez

Size (Degrees ²) Meaning Classification 386 hair of Berenice object

About 243 B.C. Ptolemy Euergetes set out on a military expedition against the Assyrians, who had murdered his sister. Berenice, who was proud if her beautiful long golden hair, vowed to sacrifice her "amber tresses" if he returned victorious. When he did, Berenice, cut off her hair, and placed it in the temple of Aphrodite, goddess of beauty. That night the hair disappeared, enraging the king and the queen. To save the situation, and the lives of the temple priests, Conon the court astronomer, announced that Berenice’s gift had received such favor that Aphrodite had taken the hair and placed it in the sky for all to admire.

Messier Objects in Coma Berenices: M-53 M-64 M-85 M-88 M-91 M-98 M-99 M-100

Name Abbreviation Pronunciation

Corona Australis CRA cuh ROW nuh aw STRAY lus

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Size (Degrees ²) Meaning Classification 128 southern crown object

Corona Australis was one of the original 48 constellations named by 2nd century astronomer Ptolemy. It is said to be the crown worn by the centaur Chiron.

Name Abbreviation Pronunciation

Corona Borealis CRB cuh ROW nuh BOR ee AL us

Size (Degrees ²) Meaning Classification 179 northern crown object

In classical mythology, this constellation is known to be the crown of Ariadne. Ariadne was the daughter of Minos, king of Crete. Every year Minos levied a tribute on Athens, requiring that the city-state send home seven each of its most beautiful maidens and youths to sacrifice to the Minotaur, a creature that was half man and half bull. The Minotaur lived beneath the palace of Knossos in the infamous Labyrinth, a maze from which no one could escape. One year Theseus, son of the King of Athens, was among the youths. When Ariadne saw him she fell in love and secretly gave him a sword and a ball of string. Theseus unwound the string as he went into the Labyrinth, slew the Minotaur with the sword, and found his way out following the sting again. Theseus fled Crete with Ariadne, and on their way to Athens the couple stopped at the island of Naxos. Mysteriously, Theseus then abandoned Ariadne, who wept for her lost love. The god Dionysus in human form but wearing a crown, found her and fell in love with her. She refused to marry him, saying she was fed up with mortal men. Dionysus told her he was a god, but she did not believe him, whereupon he took off his crown and flung it into the sky. There its jewels began to sparkle as stars, forming Corona Borealis, a tribute to Ariadne. To the Shawnee Indians, Corona Borealis was a circle of star-maidens dancing in the sky. The circle is not complete because one of the maidens left to go to Earth to live with a mortal warrior, Algon. She later grew homesick and returned to the sky, taking along her son. Later still the sky gods agreed to bring Algon into the sky, In some legends he is thought to be the nearby star Arcturus. To the Arabs, these stars formed a cracked bowl or platter. To Australian aboriginals, this constellation was a boomerang.

Name Abbreviation Pronunciation

Corvus CRV COR vus

Size (Degrees ²) Meaning Classification 184 crow animal

According to myth, one day the god Apollo sent the raven Corvus for a cup of spring water. Near the spring Corvus spied a green fig, so he sat down and waited until it ripened. To explain his tardiness Corvus returned to Apollo with the cup (Crater ) of spring water, and a water serpent, Hydra, in his claws, claiming he had been attacked by the serpent and thus delayed. Apollo, seeing all, knew the truth and so banished all three to the sky. Corvus now sits within sight of the cup of water, but he

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can never drink, because it is guarded by the serpent. According to another myth Apollo had an affair with Coronis, the daughter of a king. They had a son, Asclepius, the founder of medical science, who was immortalized in the sky as the constellation Ophiuchus. Apollo became suspicious that Coronis was unfaithful to him and sent his spy, Corvus, then of silver plumage, to observe. Indeed, Corvus reported back, Coronis was having an affair. In a rage, Apollo slew Coronis, and consigned Corvus to Hades and turned his feathers black. To the Arabs these stars were a tent. Mariners sometimes call them "the sail", for they resemble a gaff-rigged sail.

Name Abbreviation Pronunciation

Crater CRT KRAY tair

Size (Degrees ²) Meaning Classification 282 goblet object

Crater is the cup carried by Corvus the crow, to Apollo.

Name Abbreviation Pronunciation

Crux CRU KRUKS

Size (Degrees ²) Meaning Classification 68 southern cross object

Crux is a modern constellation, and is the smallest constellation in the sky.

Name Abbreviation Pronunciation

Cygnus CYG SIG nus

Size (Degrees ²) Meaning Classification 804 swan animal

Cygnus the swan, was not always a swan. Greek legend tells a tragic story of Apollo’s son, Phaeton, who tried to drive Apollo’s chariot across the sky. Apollo warned him not to drive to close to the Earth lest he set it on fire. Phaeton lost control of the wild horses, and to spare the Earth a fiery destruction, Zeus threw a lightning bolt at the young boy, killing him instantly. The horses climbed higher into the sky, scorching a path that became the Milky Way. Phaeton fell into the river Eridanus. Cygnus dove repeatedly into the river to try to retrieve the body of his friend but failed. Zeus was so impressed with Cygnus’ devotion to his Phaeton that he turned him into a swan, enabling him to dive more easily. Cygnus was eventually rewarded for his gallantry by a prominent place in the summer skies within the cloudy path of the Milky Way.

Messier Objects in Cygnus: M-29 M-39

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Name Abbreviation Pronunciation

Delphinus DEL del FEE nus

Size (Degrees ²) Meaning Classification 189 dolphin animal

One story has it that when Poseidon (Neptune) was courting the mermaid Amphitrite, he rode on the back of a dolphin. When she agreed to become his wife, Poseidon placed the dolphin in the sky in gratitude for his help. Herodotus relates another story, about the Greek poet Arion, who was exceedingly skilled at playing the harp like kithara. Periander, king of Corinth, sent Arion to Italy to play in a contest. Arion won the contest, and was richly rewarded, whereupon he chartered a ship to take him home. The crew, however, hoping to rob Arion of his treasure, attempted to throw him overboard. Arion asked to be allowed to play one last tune. He played so beautifully that he attracted a pod of dolphins to the ship, where upon Arion leapt overboard and landed on the back of one of them, who carried him home to Corinth. The seamen, thinking him lost, continued on to Corinth. Arion had arrived first and told Periander of their crime. When the ship arrived, Periander had the entire crew killed, and Arion’s prize money was returned. The gods placed a figure of a dolphin in the sky to commemorate the event.

Name Abbreviation Pronunciation

Dorado DOR dor AY doe

Size (Degrees ²) Meaning Classification 179 dolphinfish animal

Dorado is a modern constellation first appearing in Johann Bayer’s 1603 star atlas. Dorado contains the south ecliptic pole.

Name Abbreviation Pronunciation

Draco DRA DRAY coe

Size (Degrees ²) Meaning Classification 1083 dragon animal

Draco has stood for all the dragons of mythology, from Tiamat of the Sumerians to the monster slain by Saint George. In all myths the dragon symbolized anarchy and chaos. Draco’s origins probably rest with the ancient story of the Babylonian goddess Tiamat, who found herself challenged by the new gods. She created fearsome monsters to help her and in fact turned herself into a dragon. The hero Marduk defeated her by commanding strong winds to blow into the dragon’s mouth splitting her body. One half of Tiamat then became the sky, the other half became the earth. From that story the Greeks derived their myth of the battle of the ancient Titans with the newer gods of Olympus. In the conflict a dragon attacked Athena. She grabbed the creature and flung it up into the sky, where its body wound around the axis of the world, the celestial north pole.

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In another Greek story, Draco was the dragon that watched over the Golden Apples of the Hesperides, the procurement of which was one of the Twelve Labors of Hercules. To the ancient Indians Draco was a crocodile. To the ancient Egyptians it was a crocodile or a hippopotamus. The constellation has even been identified with a dragon from the German epic the Nibelungenlied.

Name Abbreviation Pronunciation

Equuleus EQU ee QWU lee us

Size (Degrees ²) Meaning Classification 72 little horse animal

This constellation is said to have been named by the Greek astronomer Hipparchus. It is the second smallest constellation.

Name Abbreviation Pronunciation

Eridanus ERI ih RID un us

Size (Degrees ²) Meaning Classification 1138 celestial river object

These faint stars have ben known as a river since ancient times, and have represented famous rivers such as the Nile and the Euphrates.

Name Abbreviation Pronunciation

Fornax FOR FOR nax

Size (Degrees ²) Meaning Classification 398 furnace object

This constellation was mapped out by Nicolas-Louis de Lacaille circa 1750.

Name Abbreviation Pronunciation

Gemini GEM JEM in ee

Size (Degrees ²) Meaning Classification 514 twins person

In classical mythology, these stars represent the twins Castor and Pollux, who were hatched from an egg borne by Leda after she was seduced by Zeus in the guise of a swan. Their sister was Helen of Troy. In ancient Rome Castor and Pollux were sometimes confused with Romulus and Remus, legendary founders of Rome. The twins were raised by the wise centaur Chiron, represented by the constellation

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Centaurus, and later joined Jason, also brought up by Chiron, when he set out on the Argo in search of the Golden Fleece. In commemoration of their helping to calm a terrible storm during the voyage, Castor and Pollux are sometimes considered the patrons of mariners. In China the two stars we call Castor and Pollux are associated with yin and yang, the dual forces of nature.

Messier Objects in Gemini: M-35

Name Abbreviation Pronunciation

Grus GRU groose

Size (Degrees ²) Meaning Classification 366 crane animal

This is a modern constellation mapped out by Johann Bayer in 1603.

Name Abbreviation Pronunciation

Hercules HER HER cue LEES

Size (Degrees ²) Meaning Classification 1225 Hercules person

In Greco-Roman mythology, Hercules is the half mortal son of Jupiter (Zeus) and the princess Alcmene. Jupiter’s ever jealous wife Juno (Hera) sent serpents to kill the baby Hercules in his crib. The child, with astonishing strength, managed to strangle them, and grew up to become the strongest of men. Thanks to the scheming of his hateful stepmother, Juno, Hercules became indentured to King Eurystheus. To gain his freedom he had to perform the famous Twelve Labors, the first of which was to kill the Nemean Lion, a fierce creature of impenetrable hide who had fallen from the Moon and was laying waste to the valley of Nemea. Hercules succeeded in strangling the beast, whereupon Jupiter place the lion in the sky as the constellation Leo. Hercules’ next task was to kill the many headed monster, the Hydra, which also became a constellation. Among his other challenges was subduing the Cretan Minotaur, who some say is the origin of the constellation Taurus. After his release from servitude the tireless Hercules accomplished many other noble deeds. One myth credits him with killing the eagle that devoured the liver of the Titan Prometheus who had stolen fire from the gods and given it to humankind. Later Hercules later won the hand of the beautiful maiden Deianeira. One day she was kidnapped by the centaur Nessus, but Hercules, hearing her cries, shot the centaur with an arrow. Dying, Nessus gave Deianeira a drop of his blood, telling her, untruthfully, that a touch of it would restore Hercules’ love if his affections ever strayed. Later, thinking her husband was losing interest in her, Deianeira put the drop on his tunic. When Hercules donned the garment, the blood burned into his skin, causing him terrible torment. Seeing what she had done, Deianeira hanged herself, and Hercules, in anguish, incinerated himself. His father, Jupiter, then placed him in the sky.

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Messier Objects in Hercules: M-13 M-92

Name Abbreviation Pronunciation

Horologium HOR HOR oh LOW gee um

Size (Degrees ²) Meaning Classification 249 clock object

Horologium is a southern constellation mapped out by Nicolas-Louis de Lacaille circa 1750.

Name Abbreviation Pronunciation

Hydra HYA HY druh

Size (Degrees ²) Meaning Classification 1303 sea serpent animal

Hydra was a many headed monster slain by Hercules as one of the Herculean tasks. This was not an easy task since each time Hercules cut off a head of the Hydra, two more heads grew in the severed head’s place. As a solution to this problem, Hercules used a torch to cauterize each stump after he cut off that head. One head was immortal, so when Hercules cut that one off, he placed it under a huge stone where it could do no harm. After the battle, Jupiter (Zeus) placed the Hydra in the sky. Hydra is the largest constellation in the sky.

Messier Objects in Hydra: M-48 M-68 M-83

Name Abbreviation Pronunciation

Hydrus HYI HY drus

Size (Degrees ²) Meaning Classification 243 water snake animal

Hydrus is a modern constellation created by Johann Bayer and published in his 1603 atlas.

Name Abbreviation Pronunciation

Indus IND IN dus

Size (Degrees ²) Meaning Classification 294 Indian person

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atlas.

Name Abbreviation Pronunciation

Lacerta LAC luh SIR tuh

Size (Degrees ²) Meaning Classification 201 lizard animal

Lacerta is a modern constellation created by Johannes Hevelius circa 1687.

Name Abbreviation Pronunciation

Leo LEO LEE oh

Size (Degrees ²) Meaning Classification 947 lion animal

The Greeks claimed that the figure was the mythological Nemean Lion, which fell from the moon in the form of a meteor. The lion ravaged the countryside around Corinth until it was slain by Hercules .

Messier Objects in Leo: M-65 M-66 M-95 M-96 M-105

Name Abbreviation Pronunciation

Leo Minor LMI LEE oh MY nor

Size (Degrees ²) Meaning Classification 232 lesser lion animal

Leo Minor was named by Johannes Hevelius about the year 1687. It is thought that these stars represented a gazelle to the ancient Arabs. In Chinese lore they were somtimes combined with the stars of Leo to make a huge celestial dragon and, in another depiction, a chariot.

Name Abbreviation Pronunciation

Lepus LEP LEE pus

Size (Degrees ²) Meaning Classification 290 hare animal

Lepus, the hare, is hiding in the grass at the feet of the great hunter Orion, as he pursues Taurus across the sky.

Messier Objects in Lepus: M-79

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Name Abbreviation Pronunciation

Libra LIB LEE bruh

Size (Degrees ²) Meaning Classification 538 scales object

Originally part of the constellation of Scorpius, this constellation was recognized as the scales by the Romans. The two brightest stars in this constellation have names that reflect this constellations as part of Scorpius : Alpha Libra is Zubenelgenubi, is Arabic for Southern Claw; and Beta Libra is Zubeneschamali, which is Arabic for Norther Claw.

Name Abbreviation Pronunciation

Lupus LUP LU pus

Size (Degrees ²) Meaning Classification 334 wolf animal

Lupus is a constellation that, though known to the ancients, is faint and has no named stars. For centuries it was known as Therion, a wild animal of know specific kind. Some thought it was a wineskin held by Centaurus, which it adjoins.

Name Abbreviation Pronunciation

Lynx LYN links

Size (Degrees ²) Meaning Classification 545 lynx animal

This consellation was created by Johannes Hevelius around 1687.

Name Abbreviation Pronunciation

Lyra LYR LIE ruh

Size (Degrees ²) Meaning Classification 286 lyre object

Very long ago, the first civilizations of the Middle East and India saw these stars as a vulture. Vega, the brightest star in Lyra was know as the Vulture Star. Even though the Greeks saw a harp here, depictions of Lyra even centuries later often showed the harp held in the claws of a vulture.

Messier Objects in Lyra: M-56 M-57

Name Abbreviation Pronunciation

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Mensa MEN MEN suh

Size (Degrees ²) Meaning Classification 153 table object

This small constellation was formed by Nicolas-Louis de Lacaille.

Name Abbreviation Pronunciation

Microscopium MIC MY kro SCO pee um

Size (Degrees ²) Meaning Classification 210 microscope object

This constellation was formed by Nicolas-Louis de Lacaille around 1750.

Name Abbreviation Pronunciation

Monoceros MON muh NOS er us

Size (Degrees ²) Meaning Classification 482 unicorn animal

The constellation is a modern constellation formed by Jakob Bartsch around 1624.

Messier Objects in Monoceros: M-50

Name Abbreviation Pronunciation

Musca MUS MUS cuh

Size (Degrees ²) Meaning Classification 138 fly insect

This constellation was orginally named Apis, the Bee, by Johann Bayer in his 1603 atlas of stars. Later Edmond Halley called it Musca Apis, the Fly Bee, and still later Nicolas-Louis dl Lacaille named it Musca Australis, the Southern Fly. This last name was to distinguish it from the northern fly, depicted on the back of Aries, the Ram. Since the norther fly is no longer recognized as a constellation, the southern fly in now known as Musca, the fly.

Name Abbreviation Pronunciation

Norma NOR NOR muh

Size (Degrees ²) Meaning Classification 165 level object

This constellation was created by Nicolas-Louis de Lacaille.

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Name Abbreviation Pronunciation

Octans OCT OCK tans

Size (Degrees ²) Meaning Classification 291 octant object

This constellation was created by Nicolas-Louis de Lacaille around 1752.

Name Abbreviation Pronunciation

Ophiuchus OPH OH fee U kus

Size (Degrees ²) Meaning Classification 948 serpent handler person

Ophiuchus is usually identified as Asclepius, a legendary physician known as the god of medicine. Asclepius was the son of Apollo and Coronis and was educated by Chiron (Centaurus ). It is said that Hippocrates, the famous Greek physician and the father of medicine was his 15th grandson. According to legend, of day Asclepius killed a snake, but to his surprise another snake arrived and revived its companion with herbs. As his medical skills grew, Asclepius even learned how to revive the dead. This knowledge worried Hades, god of the underworld, who feared that his domain would not receive any new souls. Hades persuaded his brother Zeus to kill Asclepius with a thunderbolt and to decree that all mortals must one day die. Zeus did strike Asclepius dead, but to honor his skills as a healer Zeus placed Asclepius in the sky with his serpents.

Messier Objects in Ophiuchus: M-9 M-10 M-12 M-14 M-19 M-62 M-107

Name Abbreviation Pronunciation

Orion ORI oh RYE on

Size (Degrees ²) Meaning Classification 594 hunter person

In Greco-Roman mythology, the character Orion was a famed hunter, but he was boastful and went so far as to claim that no beast could kill him. To teach Orion a lesson, the goddess Hera sent a tiny scorpion to sting him. Orion smashed the scorpion with his club but not before it had stung him fatally. Orion and the scorpion were placed in the heavens on opposite sides of the sky. When Scorpius rises, Orion sets, and vice versa; these enemies are never seen together in the sky. In another legend Orion, the son of Poseidon, was said to have been a great hunter. Artemis, goddess of the Moon and the hunt, fell in love with him and neglected her duties of lighting the night sky. Her fellow gods and goddesses pleaded with her to no avail. One day her twin brother, Apollo, the sun god, saw Orion bathing in the seas far out from shore. Apollo shined the light of the sun so brightly that Orion became just a dark blur among the brilliantly sparkling waves. Apollo then called his sister and challenged her to hit the black shape so far from shore with here arrow. In

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pride and anger Artemis shot her arrow, striking the object directly. When Orion’s body later washed ashore, Artemis realized what she had done. In grief she took his body and placed it in the sky, together with his hunting dogs, and marked it with bright stars. Having slain her lover, she was inconsolable and lost all interest in life; and that is why, ever since, the Moon has been cold and lifeless. Orion, however, quite quickly recovered and to this day he chases the Pleiades - seven lovely nymphs found in the constellation Taurus - around the sky, just as he had chased them on Earth.

Messier Objects in Orion: M-42 M-43 M-78

Name Abbreviation Pronunciation

Pavo PAV PAY voh

Size (Degrees ²) Meaning Classification 378 peacock animal

This is one of the constellations published in Johann Bayer’s 1603 atlas.

Name Abbreviation Pronunciation

Pegasus PEG PEG uh sus

Size (Degrees ²) Meaning Classification 1121 flying horse animal

When Perseus pursued and slew the Medusa, Pegasus was created by the blood of Medusa’s severed head mixed with the foam and sand of the sea.

Messier Objects in Pegasus: M-15

Name Abbreviation Pronunciation

Perseus PER PER see us

Size (Degrees ²) Meaning Classification 615 Perseus person

In Greek myth, Perseus was the son of Zeus and the mortal Danae. Danae’s father, having been told by an oracle that his grandson would on day kill him, set Danae and Perseus adrift in a trunk. They were rescued by a fisherman and went to live on his island. The king of that island, Polydectes, wished to court Danae, and to get Perseus out of the way he sent the youth to slay the Gorgons, three sisters so ugly that any mortal who beheld them turned to stone. The night before his departure, Minerva appeared to Perseus in a dream and gave him a shiny magic shield upon which he could look at Medusa’s reflection without being harmed. She also gave him a magic sword with which to sever the neck of Medusa. A man made sword would not do the job. Then Mercury appeared and gave Perseus winged sandals so that he could fly across the ocean to the island where the Gorgon lived in a cave. During his quest,

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Perseus found the three nymphs of the North, who gave him a magic helmet that would make him invisible and a magic pouch into which to place the severed head. Armed with the magic of the gods, Perseus found the island of the Gorgon Medusa. Her cave was guarded by two sisters who never slept. Perseus donned his helmet and crept quickly past them. Medusa lay asleep on the floor of the cave. Perseus raised his shield high and, watching her reflection in the dim light, he backed up to her. Then, with on mighty blow of the sword, he severed the head of Medusa. He picked up the head and placed it in the pouch. As he left the cave and walked down to the shore, a trail of blood was left behind. From Medusa’s spilled blood, Pegasus was born. Perseus mounted the winged horse and headed back to Greece. Fleeing the other Gorgons, Perseus came upon King Atlas, who refused him aid. Glancing at the head of Medusa, Atlas turned into a mountain of stone and thereafter had to bear the weight of the heavens on his shoulders. Continuing his flight, Perseus came upon the princess Andromeda, the chained maiden, and rescued her from Cetus, the sea monster. Later in his life, Perseus, throwing the discus in an athletic contest, struck and killed a spectator. That unfortunate being turned out to be his grandfather, and the prophecy that he would be killed by his grandson was fulfilled, in spite of all the old man’s efforts.

Messier Objects in Perseus: M-34 M-76

Name Abbreviation Pronunciation

Phoenix PHE FEE nix

Size (Degrees ²) Meaning Classification 469 Phoenix animal

Phoenix first appeared in the 1603 star atlas of Johann Bayer. The Arabs had called this region along the river Eridanus Al Zaurak, the Boat, and also Al Rial, the Young Ostriches.

Name Abbreviation Pronunciation

Pictor PIC PIK tor

Size (Degrees ²) Meaning Classification 247 painter person

This constellation was formed in the 1750s by Nicolas-Louis de Lacaille.

Name Abbreviation Pronunciation

Pisces PSC PIE ceez

Size (Degrees ²) Meaning Classification 889 fishes animal

The Greeks and Romans recognized two fish in these stars. They were said to be

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stream, turned into fish, and swam away to safety. They tied their tails together so they wouldn’t be separated.

Messier Objects in Pisces: M-74

Name Abbreviation Pronunciation

Piscis Austrinus PSA PIE sys aw STREE nus

Size (Degrees ²) Meaning Classification 245 southern fish animal

The constellation Piscis Austrinis has been known since classical Greek and Roman times but probably goes back even further, to an ancient Syrian constellation representing the god Dagon. It has occasionally been shown as two fish, but it is more commonly seen as a single fish, sometimes drinking from a stream of water poured from the jar held by Aquarius .

Name Abbreviation Pronunciation

Puppis PUP PUP iss

Size (Degrees ²) Meaning Classification 673 stern object

These stars form the stern of poop deck of the great celestial ship Argo. South of Puppis is Carina, the Keel, and just to the east are Pyxis, the Compass, and Vela, the Sail.

Messier Objects in Puppis: M-46 M-47 M-93

Name Abbreviation Pronunciation

Pyxis PYX PIK sis

Size (Degrees ²) Meaning Classification 221 compass object

Nicolas-Louis de Lacaille formed this small constellation from stars that had been part of the ship Argo.

Name Abbreviation Pronunciation

Reticulum RET ruh TIK u lum

Size (Degrees ²) Meaning Classification 114 net object

This constellation was formed by Nicolas-Louis de Lacaille about 1752.

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Name Abbreviation Pronunciation

Sagitta SGE suh JIT uh

Size (Degrees ²) Meaning Classification 80 arrow object

Sagitta has been identified with just about every famous arrow in mythology. It has been said to be the arrow that killed the eagle of Zeus, the arrow shot by Hercules at the Stymphalian Birds, and the one with which Apollo slew the Cyclops. It has also been said to represent Cupid’s arrow. Sagitta is the third smallest constellation.

Messier Objects in Sagitta: M-71

Name Abbreviation Pronunciation

Sagittarius SGR SAJ ih TAR ee us

Size (Degrees ²) Meaning Classification 867 archer person

This is a large constellation that was probably first associated with Nergal, the arrow shooting god of war, by Sumerian peoples of the Euphrates Valley. It was known by the Greeks as the archer, and later came to be identified as a satyr, or centaur.

Messier Objects in Sagittarius: M-8 M-17 M-18 M-20 M-21 M-22 M-23 M-24 M-25 M-28 M-54 M-55 M-69 M-70 M-75

Name Abbreviation Pronunciation

Scorpius SCO SKOR pee us

Size (Degrees ²) Meaning Classification 497 scorpion insect

This constellation is supposed to be the tiny scorpion that killed Orion with its sting and was placed in the sky to memorialize the event.

Messier Objects in Scorpius: M-4 M-6 M-7 M-80

Name Abbreviation Pronunciation

Sculptor SCL SCULPT tor

Size (Degrees ²) Meaning Classification 475 sculptor person

This modern constellation was formed by Nicolas-Louis de Lacaille.

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Name Abbreviation Pronunciation

Scutum SCT SKU tum

Size (Degrees ²) Meaning Classification 109 shield object

This modern constellation was created by Johannes Hevelius in 1690, in honor of King John III Sobieski of Poland, and was supposed to represent his coat of arms.

Messier Objects in Scutum: M-11 M-26

Name Abbreviation Pronunciation

Serpens SER SIR pens

Size (Degrees ²) Meaning Classification 637 snake animal

Serpens is the only constellation that is in two separate parts. Serpens Caput (Head of the Snake) is 429 square degrees. Serpens Cauda (Tail of the Snake) is 208 square degrees. The two parts of this constellation are separated by Ophiuchus .

Messier Objects in Serpens: M-5 M-16

Name Abbreviation Pronunciation

Sextans SEX SEX tans

Size (Degrees ²) Meaning Classification 314 sextant object

This constellation does not represent a mariner’s sextant, but the larger astronomical sextant used by Johannes Hevelius to compile one of the first accurate star maps.

Name Abbreviation Pronunciation

Taurus TAU TAW russ

Size (Degrees ²) Meaning Classification 797 bull animal

Greek legend has it that this group of stars is Zeus in the disguise of a white bull with golden horns; in this form he seduced and abducted the beautiful Europa. When Europa seated herself on the bull’s back, he swam away with her to Crete, which is why we see only the animal’s forequarters in the constellation. Taurus is also thought to be charging Orion the hunter, who lies to the east.

Messier Objects in Taurus: M-1 M-45

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Name Abbreviation Pronunciation

Telescopium TEL tel uh SCO pee um

Size (Degrees ²) Meaning Classification 252 telescope object

A modern constellation formed by Nicolas-Louis de Lacaille.

Name Abbreviation Pronunciation

Triangulum TRI tri AN gue lum

Size (Degrees ²) Meaning Classification 132 triangle object

This group of stars has been recognized since classical times. The Romans know this constellation as Deltotum. It was in this consetellation that Giuseppe Piazzi, on January 1, 1801, discovered the first asteroid.

Messier Objects in Triangulum: M-33

Name Abbreviation Pronunciation

Triangulum Australe TRA tri AN gue lum aw STRAY lee

Size (Degrees ²) Meaning Classification 110 southern triangle object

A modern constellation formed by Johann Bayer in his 1603 star atlas.

Name Abbreviation Pronunciation

Tucana TUC too CAY nuh

Size (Degrees ²) Meaning Classification 295 toucan animal

A modern constellation formed by Johann Bayer in his 1603 star atlas.

Name Abbreviation Pronunciation

Ursa Major UMA OOR suh MAY jor

Size (Degrees ²) Meaning Classification 1280 great bear animal

Our best known legend about Ursa Major comes from Greek mythology. According to this legend, the king of the gods, Zeus, fell in love with a beautiful woman named

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Callisto. When Zeus’ wife Hera learned of the affair, she changed Callisto into a bear. This bear roamed the forest until one day she happened upon a young and handsome hunter whom she recognized as her own son, Arcas. Callisto raised up on her hind legs to embrace her child, but Arcas saw only a bear and raised his spear. In the nick of time, Zeus intervened, changing Arcas into a bear. Then he grasped Callisto and her son by their tails and flung them into the sky, to become our constellations of the large and small bears. This explains why the celestial bears have such long tails, in contrast to their earthly counterparts. Some North American Indian tribes saw things differently. They also pictured bears in Ursa Major, and the nearby constellation Ursa Minor, as evidenced by the names frequently used to describe them, Okuri and Paukuawa - both meaning "bear". But in Iroquois mythology, all bears once had long tails. The earthly bear lost its tail attempting to show it off, using the tail to fish through a hole in an iced over lake. The bear’s tail froze and fell off, and now all Earthbound bears mimic this ancient bear with its stumpy tail. A Blackfoot Indian legend tells of an elder daughter of a large family. The daughter fell in love with a grizzly bear. Her father was furious and ordered her brothers to kill the bear. But this was a magical bear, and before the bear died he gave some of his magic to his bride. She then turned herself into a grizzly bear, and in retaliation she destroyed her entire village, killing her mother and father. She began chasing her eight brothers and sisters, but one brother had magic of his own. He shot an arrow into the sky, and instantly all eight children followed it to become stars. The seven oldest children became the seven stars forming the Big Dipper. The youngest child was frightened, and she can be seen as the dim star Alcor, huddling close to the star Mizar.

Messier Objects in Ursa Major: M-40 M-81 M-82 M-97 M-101 M-102 M-108 M-109

Name Abbreviation Pronunciation

Ursa Minor UMI OOR suh MY nor

Size (Degrees ²) Meaning Classification 256 lesser bear animal

Ursa Minor was not recognized as a constellation until about 600 B. C., when it was decribed by the Greek astronomer Thales.

Name Abbreviation Pronunciation

Vela VEL VEE luh

Size (Degrees ²) Meaning Classification 500 sails object

Vela represents the sail of the ship Argo (Argo Navis), the huge ancient southern constellation that was divided into several smaller constellations by Nicolas-Louis de Lacaille in the 1750s.

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Name Abbreviation Pronunciation

Virgo VIR VUR go

Size (Degrees ²) Meaning Classification 1294 maiden person

Virgo is the only female figure amoung the constellations of the zodiac. It is also one of the oldest constellations and has assumed the identity of just about every important female deit since history has been recorded. In particular, Virgo has been identified with goddesses of fertility, of agriculture, and of the earth. Virgo is the second largest constellation in the sky.

Messier Objects in Virgo: M-49 M-58 M-59 M-60 M-61 M-84 M-86 M-87 M-89 M-90 M-104

Name Abbreviation Pronunciation

Volans VOL VO lans

Size (Degrees ²) Meaning Classification 141 flying fish animal

A modern constellation formed by Johann Bayer in his 1603 star atlas.

Name Abbreviation Pronunciation

Vulpecula VUL vul PEK u luh

Size (Degrees ²) Meaning Classification 278 fox animal

Vulpecula is a modern constellation formed in 1690 by Johannes Hevelius.

Messier Objects in Vulpecula: M-27

Source: http://www.seds.org/messie/m-names.html

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