INST 2403
STUDY GUIDE for Midterm 3
FALL 2014
Form of Exam





About 35 questions
Mostly multiple choice
Few short answer questions
You have the whole class period; this should be ample time
Scantron sheets are used
Topics (also see syllabus)











Greenhouse Effect
Stellar Parallax
EM Radiation
Atomic Spectra
The Sun
Stars
Absolute & apparent magnitudes
Hertzsprung-Russell diagrams
Interstellar Medium
Stellar Lifecycle
NOT: Dead Stars (Black Holes, Neutron Stars)
Suggestions





Review textbook readings, online Powerpoint slides
Revisit the Warm-Up questions
Look over the activities
Take another look at the homework questions. In particular, check the solutions after you
committed to an answer
It might help to go to the library and study other astronomy texts. Often reading an
independent explanation in slightly different wording helps to understand a complex
concept.
Sample Questions
1. Compare the power radiated by two stars A & B. The temperatures of the stars are related: T B = 3 TA.
How do the power outputs P of the stars compare?
a. PA = PB
b. PA = 1/216 PB
c. PB = 81 PA
d. PB = 3 x 104 PA
e. None of the above.
1
2. Consider the two blackbody spectra shown in Figure 2a, where the
energy output per second is plotted as a function of the wavelength.
The colors in the visible range are represented by their first letter
(v=violet, r=red, etc.) What can we conclude about the properties of
stars A and star B?
a.
b.
c.
d.
Star A has a smaller peak frequency than star B.
Star A has a longer peak wavelength than star B.
Star A is cooler than star B.
Star A radiates more red light than star B.
Star A and star B have the same temperature.
e.
3. The peak frequency of an object A’s blackbody curve is half as large as the one of B’s curve, hence
a. TA=TB
b. 2TA=TB
c. TA=2TB
d. 4TA=16TB
4. A cold, low density cloud of gas put in front of a light bulb will produce what type of spectrum?
a) Continuous spectrum
b) Emission spectrum
c) Absorption spectrum
d) No spectrum
e) Kirchhoff spectrum
5. Which of the following magnitudes is the brightest?
a. 15.0 m
b. –1.5m
c. 3.5m
d. 12 m
e. –12 m
6. Red Giants sit where in the Hertzsprung-Russell diagram?
a. upper left corner
b. lower left corner
c. upper right corner
d. lower right corner
e. none of the above
7. Main-sequence stars with a mass smaller the sun …
a) …live longer
b) …have larger radii
c) …have a larger luminosity
d) …have a larger surface temperature
e) …have a larger core temperature
8. Two stars have the same chemical composition, spectral type, and luminosity class, but one is 4 light
years from the Earth and the other is 40 light years from the Earth. The farther star appears to be …
a) 100 times fainter.
b) 10,000 times fainter.
c) 100,000,000 times fainter.
d) the same brightness since the stars are identical.
2
9. Stars in the lower right corner of a Hertzsprung-Russell diagram
a. have small radii, large luminosity
b. large mass and small luminosity
c. high temperature and small life expectancy
d. low temperature and high life expectancy
e. none of the above
10. What is the single most important characteristic in determining the course of a star's evolution?
a. Absolute brightness
b. Distance
c. Surface temperature
d. Mass
e. Radius
11. Two stars have the same temperature, but one has four times the radius of the other star. How much
brighter is the larger star?
a. 4 times
b. 16 times
c. 64 times
d. 1/64 as bright
e. None of the above
12. A star has an absolute magnitude of 3.6M and an apparent magnitude of -0.2m. What can you say
about its distance from Earth?
a. it is closer than 10pc
b. it is 10pc away
c. it is farther than 10pc
d. its is much farther than 10pc
e. Nothing, since we do not know the luminosity of the star.
13. Consider two stars with 2 solar masses (star A) and 0.5 solar masses (star B). Which is a true
statement?
a. Star A will live longer because it has more hydrogen to fuse.
b. Star A will live 2 times shorter than star B.
c. Star A will live 2 times longer than star B.
d. Star A will live more than 2 times longer than star B.
e. None of the above.
Short Answer Questions [3 points each]
(Please use the back side of the computer sheet to record your answers)
14. Explain how the method of spectroscopic parallax works.
15. Why are main sequence stars the brighter the hotter they are, while, on the other hand, red giants are
so bright even though they have a relatively cool surface?
16. How does the luminosity, radius, mass and temperature of a star change as it develops from a main
sequence star into a red giant?
3
List of Warm-Up Questions
Warm-up #22: based on Section 5.3
1. Describe, in your own words, the greenhouse effect, i.e. how the atmosphere of a planet affects the
temperature of the planet’s surface.
Warm-up #23: based on Section 10.1: “The Solar Neighborhood”
1. Compare the Stellar Parallax (Fig. 10.1) with the parallax described in section 0.4. What is the same,
what is different?
2. Why are the background stars used in the Stellar Parallax not moving, even though Earth moves 300
million km between January and July?
Warm-up #24: based on Sections 2.1-2.5
1. What is a wave and what quantities/properties characterize it?
2. What is electromagnetic radiation?
3. What is the Blackbody Curve and how does it depend on temperature?
Warm-up #25: based on Sections 2.5+2.6
1. What is a “spectrum”?
2. Where do the lines in a spectrum come from?
Warm-up #26: based on Sections 2.6-2.8
1. Explain the Doppler effect.
2. Why is it useful?
Warm-up #27: based on Chapter 9 “The Sun”
1. Explain hydrostatic equilibrium.
2. Explain the main idea of nuclear fusion, i.e. how is the sun producing so much energy?
Warm-up #28: based on Chapter 10 “Measuring the Stars”
1. How are a star’s color, temperature and spectral class related?
2. What is a Hertzsprung-Russell diagram?
Warm-up #29: based on Chapter 11 “The Interstellar Medium”
1. What is the difference between gas and dust, and how do we “see” clouds of them in space?
2. Describe, very crudely, how stars (say of one solar mass) form, and how the star “moves” in a
Hertzsprung-Russell diagram as it goes through its early life stages.
Warm-up #30: based on Chapter 12 “Stellar Evolution”
1. Why do stars leave the Main Sequence?
2. Describe, very crudely, how a star (say of one solar mass) changes after it leaves the Main Sequence.
3. What is a supernova and why does it occur?
Warm-up #31: based on Chapter 12 “Stellar Evolution”
1. Briefly describe the cycle of stellar evolution.
2. What, if anything, is different in the next generation of stars?
4