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Review questions for PS 224 mid-term!
This is a summary of the concepts we covered in class till the end of Week 7 (Oct 9). Refer to
your notes (and the book) for a more comprehensive list. !
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You should be comfortable with discussing and explaining these concepts. !
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The midterm will be based on what we covered in class and not on this review sheet. !
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You do not need to memorize equations or constants. !
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Week 1!
1. What is astronomy? Why do we study astronomy?!
2. Why can you not see the Milky Way with the naked eye? !
1. How does a telescope work?!
2. Compare human eye vs. telescope!
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Week 2!
1. What causes seasons?!
2. What causes eclipses?!
3. Why do stars rise and set?!
4. What is the reasons for phases of the moon?!
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Week 3: Orbital Motion, Kepler’s Laws, & Gravity!
1. define: speed, velocity, acceleration, momentum!
2. mass vs. weight!
3. Conservation of energy (kinetic and potential energy)!
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4.
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5.
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4⇡ 2
a
⇥
Newton’s version of Kepler’s third law: ! P =
G
M1 + M2
2
Newton’s law of Gravitation: !
Fg =
GM1 M2
d2
Week 4/5: Light & its Interaction with Matter!
1. What is light? What is electromagnetic radiation?!
2. How does light interact with matter?!
Short Answer: electrons absorb photons (causing absorption lines) and reradiate them at
a later time (causing emission lines). Light can also be transmitted and reflected/
scattered.!
3. How do these interactions tell us about astronomical objects?!
1. What are the different things we can learn by looking at a spectrum?!
4. What is the physics behind these interactions?!
Short answer: electrons moving between different, discrete energy levels.!
How can we tell a given photon is from a particular element or energy level?!
5. How do we collect light?!
6. Thermal Radiation & Blackbody spectrum!
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1. Everything at T > 0 K emits light, at all wavelengths!
2. absorption vs. emission spectra!
3. Laws of Thermodynamics!
1. Stefan-Boltzmann Law: Hotter objects emit more light per unit area at all frequencies.!
power emitted = σ T4!
2. Wien’s Law: Hotter objects emit photons with a higher average energy.!
max
⇡
2, 900, 00
nm
Tef f (K)
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4. Temperature is the average energy of the particles in the system. !
5. Doppler effect: what does it tell us about stars?!
Vrad
=
c
shif t
rest
rest
6. Why do we need to put telescopes in space?!
Week 6: Sun & Solar System!
1. What are some interesting characteristics about the members of our Solar System?!
2. How did the Solar System form?!
1. What are the characteristics that help us understand the formation?!
2. What are the exceptions?!
3. How can we measure the age of the Solar System?!
4. What properties of the Sun can we directly measure?!
5. What is the relation between magnetic field, activity, and sunspots?!
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Week 7: Stars!
1. How do we measure stellar luminosity?!
1. How do we measure stellar distances? What is parallax? !
2. How do we measure stellar temperatures?!
3. How do we measure stellar mass?!
4. What is the Hertzsprung-Russell (H-R) diagram?!
1. What is the main-sequence?!
2. What are the giants and white dwarfs?!
3. Make sure you know how to read off mass, color. temperature, and luminosity from the
H-R diagram.