The Study of the Sun ES 24 Astronomy 2. The Study of Light Astronomy 2 ES 24.1 Day.

The Study of the Sun

ES 24

Astronomy 2

The Study of Light

Astronomy 2

ES 24.1

Day

Opener – Quick Write• We are going to write for exactly one minute on

a certain topic (to be shown once the bell rings).• You may do this in your notes.• On our opener for today, put “quick write”• Don’t pick up your pencils until I tell you to…• This is excellent practice for standardized tests

(like the ACT/MME) The purpose is for you to get ideas out of your head and down on paper. Of course, it must be related to the question. See how many words you can get in 60 seconds! We will count them at the end.

Opener – Quick Write

• Explain what the difference is between potential energy and kinetic energy, and how one can be converted to the other.

Light

• Light is very much still a mystery• Visible light is only a small part of all the

different types of light• Electromagnetic Radiation: Includes

gamma rays, X-rays, ultraviolet light, infrared rays, microwaves, radar waves, television/radio waves

• All types of light travel at the same speed (300,000 km/s)

Electromagnetic Spectrum

Electromagnetic Spectrum

What is Light?

• Light behaves in some ways like a wave and in some ways like a particle

• Waves: think of waves in the water• Wavelength: the distance from one crest

of a wave to the next• Different wavelengths = different colors• So violet and blue have very short

wavelengths, red and orange have very long wavelengths

Opener

• How much of light can we see?

• What other kinds of “light” are there? (name as many as you can remember)

Light as a Wave

• Think of dropping a rock into a completely still pool of water…what happens?

• Now think about at the beach, the breakwater…what happens to the waves?

• The same thing happens with light

• That’s why if a light is on in the hallway, it still partially lights up our room

• Light “bends”

Photons• Photons: streams of “light particles”• Because light sometimes acts like its made of

particles instead of waves• Think of very small bullets fired from a machine

gun…they have a force, they can push on matter• The force from light is called radiation pressure• Where did we hear that before???• Each photon has a specific amount of energy• Shorter wavelengths have more energy than

longer wavelengths

The Doppler Effect

• Doppler effect: the perceived change in wavelength from a source that is moving.

• Sound: When an ambulance is approaching you, the siren sounds higher in pitch (because the waves are closer together)

• Light: When an object is approaching, the light from it is appears redder than it actually is

• Astronomy: Can determine whether stars are moving toward us or away from us

Brief Review

• Is light a wave or a particle?

• How does light act like a wave?

• How does light act like a particle?

• What is the Doppler effect?

Tools for Studying Space

Astronomy (2)

ES 24.2

Day

Telescopes

• Refracting Telescopes: uses a lens to bend light

Telescopes

• Reflecting Telescopes: Uses a mirror to focus light in front of the mirror

Telescopes

• Radio Telescopes: Focus incoming radio waves

Light Continued

Astronomy 2

ES 24?

Day ?

Opener

• How does light act like a wave? Give an example (draw a picture if you want)

• What are the particles of light that carry radiant energy called?

Reflection, refraction

• Refraction: light bends through glass

• Reflection: use of mirrors

When you shine a light at a mirror, what happens? What if its at an angle?

Angle of incidence = angle of reflection

Light and Telescopes

• What if you have a mirror that is curved?

Concave Convex

(light unites) (light diverges)

Concave/convex

Concave Convex

The front of a spoonThe back of a spoon

Light

• We can only see things because light is being reflected off of them

• So when we see a blue object, its because the blue light is being reflected. All the other colors are being absorbed.

• When waves pass into a different medium (substance), they change speeds

• Why don’t they change wavelengths?• When light passes into a different medium

(substance), it is refracted (bent).• Think of light going through water…it gets bent,

distorted

Other electromagnetic waves

• Sonar is using reflected sound waves underwater

• Bats use echolocation (similar)

• Know the general order of the different types of electromagnetic waves! We’ll be getting a worksheet on it…

Waves

Astronomy 2

PS 10

Day

Waves

• Wave: Repeating movement that transfers energy through matter or space

• So the wave travels only as long as it has energy to carry

• Waves on a lake don’t actually move water…what do they move?

• Think of a boat and a bunch of waves hit it, after they pass its in nearly the same place

Mechanical Waves

• Transverse waves: matter moves at right angles to the energy (water, light, and electromagnetic waves)

• Compressional waves: matter moves in same direction as energy (springs, and sound)

Parts of a wave

Crest

Trough

Wavelength

Frequency: The # of wavelengths that pass by each second

1 Hz = 1 wavelength per second\

Amplitude: the height

Wavespeed

v = fλv = velocity (m/s)

f = frequency (Hz)

λ = wavelength (m)

If we increase f, then λ must decrease

If we increase λ, then f must decrease

If the wave passes through a medium (substance) with different density, the speed may change

Wavelength

The lowest pitched sounds humans can hear have frequency of 20 Hz. What Is the wavelength of those sound waves if their speed is 340 m/s?

Wavelength

• The speed of light is 300,000 m/s. Find the frequency of blue light (about 400 nm, or .0004 m) and of red light (about 800 nm, or 0.0008 m).

LAB – Retrograde Motion of Mars

Astronomy 2

Day

Opener

• Suppose light is reflected from a surface and you decrease the angle of incidence by 0.5 (cut it in half). What will happen to the angle of reflection?

• What color(s) wavelength is/are being reflected from a green book? What color(s) is/are being absorbed?

Retrograde Motion of Mars

• Lots of graphing

• To see how Mars moves in the night sky in relation to the stars

• You may work in groups of 3 (your choice)

• Use different colors!

• Due: Monday (but you may turn it in today if you get done)

The Sun

Astronomy (2)

ES 24.3

Day

Opener

• Draw a quick sketch of a concave surface and a convex surface.

• What effect does each surface have on light waves coming at it? (sketch it or use a one word answer)

The Sun’s Regions

Corona

Core Photosphere

Chromosphere

Chromosphere Corona

Solar Wind

• Solar wind: The streams of protons and electrons that shoot out from the sun’s corona

• Sunspots: Dark regions on the photosphere

Aurora Borealis

Nuclear Fusion

• Nuclear Fusion: how the sun gives energy

• During nuclear fusion, 4 hydrogen (H) atoms combine to form one helium (He) atom

• 4 H atoms have more mass than 1 He atom… so there’s leftover mass

• E = mc2

The Sun’s Future

• The sun can “live” about 10 billion years

• Its been around for 4.5 billion years

• So it will be around for another 5.5 billion years

4.5 billion years 5.5 billion years

10 billion years

Sun formed Sun changesNow

Our Sun

• Our sun is a main-sequence star

• We’ll learn more about this later…

• In about 5.5 billion years, it will become a red giant

• Don’t worry, we’ve got time!

Review

• Where does the sun’s energy come from?

• What are sunspots? What is solar wind?

• How long will the sun stay in its present form?

Waves Worksheet

• We’re going to do some of these in class

• Some individually, some together

• Then we’ll finish it as homework

Stars

Astronomy

ES 25

Day

Opener

• Where does the sun’s energy come from (what is the process called?)

• How much longer will the sun stay in its present form?

• What is the difference between sunspots and solar wind?

5th and 6th hours: Your Mars Lab is due today! Please turn it in!

HW – Waves Worksheet

• Go over answers in your “natural groups of four”

• The person who will read their answers for the rest of the group will be the person who….

• We’ll go over any questions in a moment, but make sure you circle any that you don’t agree on!

Stars

• Nearest star: Proxima Centari – 4.2 light years away!

• Stars are light years away!

• 1 light year = 9.5 trillion kilometers

• Color relates to temperature…think of looking into a fire, what color is the middle of the fire? The outside?

• Blue stars = very hot

• Red stars = cooler

Betelgeuse and Rigel

• Which is hotter???

Hertzsprung-Russell Diagram

• The Hertzsprung-Russell diagram shows the relationship between absolute magnitude and temperature (of stars)

• Shows dwarf stars, giants/supergiants, and main-sequence stars

• About 90% of stars on HR diagram are main-sequence

• Absolute magnitude: -10 is bright +10 is dim

HR Diagram

Some Questions for us…

• Which main-sequence stars are the brightest?

• Which are the least bright?

• Which are brighter, giants or dwarfs?

• Where is the sun?

HR Diagram Lab

• Due Wednesday

• Plot carefully! Scales are not even!

• Think about what your diagram should look like

Opener

• Suppose you are looking at two stars, one is blue and one is red. Which one is hotter?

• Where are most stars on the HR diagram (giant, dwarf, or main-sequence)?

Star death

• All stars will eventually run out of fuel…then they collapse

• Main sequence, dwarfs, and giants will all eventually “die”

• This makes sense, if they’re using nuclear fusion (H to He) eventually they’ll run out of H!

Black Holes

• What do black holes look like???• Black holes: incredibly small, but

EXTREMELY dense• They are old stars (used to be supergiants)• So they have a lot of mass in a little area• Remember more mass means more

gravity, so these have a lot of gravity• Even light can’t escape the gravity of a

black hole

Life, the Universe, and Everything

• Galaxies: groups of stars, dust, and gases

• What could hold them together??

• Gravity!

• Our sun is within one of the spiral arms of the Milky Way galaxy

Life, the Universe, and Everything

• The Big Bang Theory says the Universe began 13.7 billion years ago with a violent explosion.

• This would explain why the universe is expanding• Think of a balloon with a bunch of dots on the outside

being blown up…the dots would continually separate from each other. Or think of baking raison bread, the same thing would happen.

• Cosmic background radiation supports this theory• Cosmic waves are faint radio signals coming from

every direction in space

Quick Review

• What will happen at the end of a stars life?

• Where is our sun? (in which galaxy, and in what part?)

• According to the big bang theory, how old is the universe?

Assignment

• Finish the worksheet/lab we started yesterday

• Remember to use a ruler to help guide you!

• Ask for help!!!

• When you are done, there are a few questions about the diagram. You’ll need to refer to your notes for this.

Opener

• Quick Write: Again, 60 seconds to spend on the following prompt. Do your best, compete against yourself! Try to beat your old score, but don’t sacrifice quality!

• Also, reminder that our labs are due today! (on the HR diagram)

Opener

• Prompt: Using definitions, examples, and/or analogies, compare transverse waves to compression waves.

• Don’t forget the lab is due today! You can turn it in near the end of class.

Lab Questions

• Are the nearest stars to us necessarily the brightest? How do we know?

• Why did we not see any white dwarfs on our table?

• Why is Betelguese so bright, when it’s a cool, distant star?

Review

1. Draw a quick sketch of an HR diagram, labeling the three groups of stars. Label each axis appropriately (you don’t need a scale)

Review

2. Briefly describe how the solar system formed (what did it start with, how did the process go)

Review

3. Draw the picture below, and put as many of the different types of electromagnetic waves as you can remember on it.

Short wavelength (λ) Long wavelength (λ)

Review

• You can spend the remainder of the time working on the review packet

• Quiet atmosphere (working individually in your own seat, possibly checking your answers quietly with the person sitting next to you)

• It will be collected on Friday, but don’t count on having time tomorrow to work!

• Finish most of it tonight, then you have only a little more to do Thursday night.

• Highlight/circle the ones you don’t know

Opener

• What happens if you increase the frequency of a light wave? (What happens to the wavelength?)

• What happens if you decrease the frequency?