© 2011 Pearson Education, Inc. The Sun: Our Star A glowing ball of gas held together by its own gravity and powered by nuclear fusion
© 2011 Pearson Education, Inc.
The Sun: Our Star
A glowing ball of gas held together by its own gravity and powered by nuclear fusion
© 2011 Pearson Education, Inc.
Interactive notes---I am supplying you with a set of notes to help you study. I have taken out some slides that are mostly pictures or instructions to the class.
Please refer to the online set of notes as you study. Use
these as a tool.
© 2011 Pearson Education, Inc.
Radius: 700,000 km
Mass: 2.0 × 1030 kg
Density: 1400 kg/m3
about ¼ the earth’s density, similar to the Jovian planets
Rotation: We use sunspots to determine. Differential (faster at the equator (25 days), slower at the poles (31 days at 6o degree latitude); period about a month
Surface temperature: 5800 K (above melting point of any known material)
Apparent surface of Sun is photosphere –not a solid surface
Physical Properties ofthe Sun
The Sun is the Largest Object in the Solar System
• The Sun contains more than 99.85% of the total mass of the solar system
• If you put all the planets in the solar system, they would not fill up the volume of the Sun
• 110 Earths or 10 Jupiters fit across the diameter of the Sun
How big is the Sun?
Copyright © 2012 Pearson Education, Inc.
Let’s reduce the size of the solar system by a factor of 10 billion; the Sun is now the size of a large grapefruit (14 cm diameter).
How big is Earth on this scale?
A. an atom
B. the tip of a ballpoint pen
C. a marble
D. a golf ball
Copyright © 2012 Pearson Education, Inc.
The scale of the solar system• On a 1-to-10 billion
scale:— Sun is the size of a
large grapefruit (14 centimeters).
— Earth is the size of a tip of a ballpoint pen, 15 meters away.
Relative Distance of the Nearest Star
Copyright © 2012 Pearson Education, Inc.
Scales and Sizes In Astronomy
• Mercury’s distance from the Sun.• Is about half the Sun-Earth distance.• It is half an Astronomical Unit.
• The star Sirius is about twice as massive as the Sun• We say it has a mass of two solar masses.
• Sirius is about 25 times more luminous than the Sun.• We say it has a luminosity of twenty-five solar luminosities.
An X-ray look at the Sun.
http://bcs.whfreeman.com/universe6e/pages/bcs-main.asp?v=category&s=00110&n=01000&i=18110.07&o=|18000|01000|&ns=0
© 2011 Pearson Education, Inc.
SOHO: Eavesdropping on the Sun
SOHO: Solar and Heliospheric Observatory
Orbits at Earth’s L1 point, outside the magnetosphere
Multiple instruments measure magnetic field, corona, vibrations, and ultraviolet emissions
SunspotsSunspots
What are they?What are they?What do they do to us?What do they do to us?
Why should you even care?Why should you even care?
What is a sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity that draws off the convection of heat to the surface, thus cooling the surface.
Sunspots are usually in pairs because of the magnetic activity causing North and South poles at either of the spots.
Pic on next slide
What do sunspots do to us?
Sunspots are a main hotbed of solar flares and prominences from the sun.
These are in turn pushed by their energy into space as solar wind once they break free of the sun's gravity
These solar winds are comprised of highly charged particles hurtling towards Earth
What does that mean to you? All of those charged particles will wreak havoc with
electronics. A particularly large solar flare caused blackouts over a large portion of Canada.
The particles can also cause the Aurora Borealis over the northern latitudes, known as the Northern Lights.
On a darker note this can also cause massive disruptions to communications, GPS, and military satellites. So if a bad solar storm were to hit, it could potentially cut off your phone from Facebook, cause your car to get wrong directions, and make the Air Force shoot a missile at the wrong building.
Watch Danger Solar Flare and information about the SDO
Answer the questions on the provided sheet --be ready to discuss your answers
Online Activity of Solar activity
© 2011 Pearson Education, Inc.
Physical Properties ofthe Sun
This is a filtered image of the Sun showing sunspots, the sharp edge of the Sun due to the thin photosphere, and the corona
© 2011 Pearson Education, Inc.
SDO site a plethora of pictures and video
http://www.nasa.gov/mission_pages/sdo/main/index.html
http://sdo.gsfc.nasa.gov/
The Active Sun
1. Sunspots appear dark because they are cooler areasthey have a regular 11 year cycle
2. ProminencesHuge cloudlike structures of chromatic gasestrapped by magnetic fields
3. Solar flaressudden brightening above a sunset cluster
Auroras-display of color near poles caused by solar flares
© 2011 Pearson Education, Inc.
Interior structure of the Sun: The core is where nuclear fusion takes place
The photosphere is the visible “surface” of the Sun. Below it lie the convection zone, the radiation zone, and the core. Solar atmosphere consists of the chromosphere, the transition zone (temperature rises dramatically), and the corona.
Convection zone and Radiation zone
• Convection
-Below photosphere where the material is in constant convective motion
• Radiation– Solar energy is transported due to radiation
Photosphere
• Grainy appearance to sun when look in a telescope caused by granules, areas of hotter gases rising—last 10 minutes and new ones arise causing a convection
• 90% of sun’s surface are hydrogen
• 10% helium
ChromosphereAbove the photosphere is a thin layer of hot
gases. It is viewed during an eclipse as a thin red rim
Corona
Outermost portion of the atmosphere
Visible only when photosphere is covered
Solar wind—ionized gases that escape the gravitational pull of the sun and bombard parts of solar system, it can effect our atmosphere.
The Solar Interior
Nuclear Fusion
-Converts four Hydrogen nuclei into one helium releasing energy
energy is released because some matter is converted to energy
Causes the core to grow in size
Sun can exist in its present state another 10 billion years
• Nuclear fusion in the sun is a process by which rapidly colliding nuclei, like those of hydrogen and helium, fuse together at very high temperatures, to form nuclei of higher atomic weight.
• Nuclear fusion in the sun is a merger of smaller nuclei into heavier ones, releasing a lot of energy in the process.
What is nuclear fusion in the sun?
How it works!
• In the process of the hydrogen and helium fusing together, some mass is lost and converted into energy.
• Nuclear fusion in the sun is only possible when the repulsion between protons is overcome. – For that to happen, energy and temperature
at the suns core has to be really high.
The Suns core
• The total radius of the sun is 6.955 x 10^5 km (about 109 times the radius of Earth) – Its core extends from the center to about 1.8
km, with a temperature of 14.5 million Kelvin.
• Consider that four hydrogen atoms have a combined atomic mass of 4.032 atomic mass units whereas the atomic mass of helium is 4.003 atomic mass units, or 0.029 less than the combined mass of hydrogen. The tiny missing mass is emitted as energy as according to Einstein's equation:
E=mc^2• E equals energy, m equals mass, and c equals the
speed of light. Because the speed of light if very great (300,000 km/s), the amount of energy released from even a small amount of mass is enormous.
• The conversion of just one pinheads worth of hydrogen to helium generates more energy than burning thousand of tons of coal.
• The sun is consuming an estimated 600 million tons of hydrogen each second; about 4 million tons are converted to energy. – Even at the enormous rate of consumption, the sun
has enough fuel to last easily another 100 billion years.
– However, evidence from other stars indicates that the sun will grow dramatically and engulf Earth long before all of its hydrogen is gone.
– It is thought that a star the size of the sun can exist in its present state for 10 billion years.
Today’s Lecture Tutorial
“ The Future of the Sun and the Earth”
You will need the internet to help you with the tutorial.
https://www.youtube.com/watch?v=3MmIDYRfr0o
https://www.youtube.com/watch?v=VCgi35M8qMU
© 2011 Pearson Education, Inc.
Luminosity—total energy radiated by the Sun— can be calculated from the fraction of that energy that reaches Earth.
Solar constant—amount of Sun's energy reaching Earth—is 1400 W/m2. (W = watts)
Total luminosity is about 4 × 1026 W—the equivalent of 10 billion 1-megaton nuclear bombs per second.
Physical Properties ofthe Sun
© 2011 Pearson Education, Inc.
We can draw an imaginary sphere around the Sun so that the sphere’s surface passes through Earth’s center. The radius of this imaginary sphere equals 1 AU. The “solar constant” is the amount of power striking a 1-m2 detector at Earth’s distance. By multiplying the sphere’s surface area by the solar constant, we can measure the Sun’s luminosity—the amount of energy it emits each second.
Solar Luminosity
© 2011 Pearson Education, Inc.
Doppler shifts of solar spectral lines indicate a complex pattern of vibrations
© 2011 Pearson Education, Inc.
Solar Oscillations (a) The Sun has been found to vibrate in a very
complex way. By observing the motion of the solar surface, scientists can determine the wavelength and the frequencies of the individual waves and deduce information about the solar interior not obtainable by other means. The alternating patches represent gas moving down (red) and up (blue).
(b) (b) Depending on their initial directions, the waves contributing to the observed oscillations may travel deep inside the Sun, providing vital information about the solar interior. (National Solar Observatory)
© 2011 Pearson Education, Inc.
Sunspots come and go, typically in a few days.
Sunspots are linked by pairs of magnetic field lines.
Solar Magnetism
© 2011 Pearson Education, Inc.
Solar MagnetismSunspots originate when magnetic field lines are distorted by Sun’s differential rotation
© 2011 Pearson Education, Inc.
The Sun has an 11-year sunspot cycle, during which sunspot numbers rise, fall, and then rise again
Solar Magnetism
© 2011 Pearson Education, Inc.
This is really a 22-year cycle, because the spots switch polarities between the northern and southern hemispheres every 11 years
Maunder minimum: few, if any, sunspots
Solar Magnetism
© 2011 Pearson Education, Inc.
Solar Convection Physical transport of energy in the Sun’s convection zone. We can visualize the upper interior as a boiling, seething sea of gas. Each convective loop is about 1000 km across. The convective cell sizes become progressively smaller closer to the surface.
© 2011 Pearson Education, Inc.
Solar Granulation Typical solar granules are comparable in size to Earth’s continents. The bright portions of the image are regions where hot material is upwelling from below. The dark regions correspond to cooler gas that is sinking back down into the interior.
© 2011 Pearson Education, Inc.
Solar Spectrum A detailed spectrum of our Sun shows thousands of Fraunhofer spectral lines which indicate the presence of some 67 different elements in various stages of excitation and ionization in the lower solar atmosphere. The numbers give wavelengths, in nanometers.(Palomar Observatory/Caltech)
© 2011 Pearson Education, Inc.
What are Neutrinos?
Neutrinos are subatomic particles produced by the decay of radioactive elements and are elementary particles that lack an electric charge
Neutrinos are emitted directly from the core of the Sun and escape, interacting with virtually nothing. Being able to observe these neutrinos would give us a direct picture of what is happening in the core. Unfortunately, they are no more likely to interact with Earth-based detectors than they are with the Sun;
Observations of Solar Neutrinos
© 2011 Pearson Education, Inc.
16.7 Observations of Solar Neutrinos
Typical solar neutrino detectors; resolution is very poor
© 2011 Pearson Education, Inc.
• Main interior regions of Sun: core, radiation zone, convection zone, photosphere, chromosphere, transition region, corona, solar wind
• Energy comes from nuclear fusion; produces neutrinos along with energy
•Study of solar oscillations leads to information about interior
•Absorption lines in spectrum tell composition and temperature
• Sunspots associated with intense magnetism
• Number of sunspots varies in an 11-year cycle
• Large solar ejection events: prominences, flares, and coronal ejections
Summary of the sun