Download Sample exam 2

Astronomy 115
Sample exam 2 (previous five weeks)
Open book, exercises and notes, no collaboration. You have 50 minutes.
Short answer — answer all questions.
1. Give one piece of information you have learned about your open cluster and a full
bibliographic citation for the source of that information. At a minimum, the citation
should contain the names of the author(s), the title of the work or URL, and the
publication date.
2. State “similar” or “different” when comparing a neutron with a proton.
a. Electrical charge
b. Mass
3. State “absorption” or “emission” for the best type of spectrum to find out the
information requested:
a. The identity of a hot gas in a nebula
b. The identity of a cool gas in a star’s “atmosphere”
4. If the Sun ceased fusion, which of the following would first stop being detected on
Earth?
a. Visible light
b. UV light
c. Neutrinos
d. Solar wind
5. Order the following methods by limiting range (1 = closest, 3 = furthest):
Main-sequence fitting
Parallax
Cepheid variable
6. A negative B-V index for a star means (circle one):
a. a cool star
b. a bright star
c. a hot star
d. a dim star
7. Stars form from (choose all that apply):
a. dark nebula
b. molecular clouds
c. H II regions
8. The Jeans Criterion equation is:
k T
where RJ is the Jeans length, and so forth.
G m2 n
If the temperature of the nebula increases, the Jeans length:
RJ =
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a. increases b. decreases c. stays the same
d. cannot tell
d. planetary nebula
9. The Sun is said to be in hydrostatic equilibrium. Which two forces compete to
maintain this equilibrium?
10. When the Sun enters its red giant phase (the unstable portion of its life cycle), it will
(choose one):
a. move from luminosity class V to class III
b. move from luminosity class I to class V
c. move from spectral type G to spectral type O
d. move from spectral type M to spectral type G
e. not change luminosity class or spectral type
Essay questions — choose three of the following questions; circle the numbers of the
ones chosen, so I know which ones to grade. Please answer each question in
sentence/paragraph format or a drawing, depending on what is asked.
11. The Sun started off its trajectory on the Hertzsprung-Russell diagram by initially
moving down and to the left as it organized into a protostar. Explain this behavior
in terms of temperature and luminosity, and give a reason for this behavior, given what
we know about stars.
12. What are the conditions necessary to initiate star formation? Give at least three
different characteristics, and how each leads to (or is needed for) star formation.
13. Globular clusters are clusters that orbit a galaxy that contain millions of M-class
stars. What does this suggest about the age of the cluster? What might you look for (and
in what part of the EM spectrum) to support your age hypothesis?
13. Suppose you are looking at the emission spectrum of gaseous helium. You
dutifully write down the wavelengths of emission. You notice a power dial on the side of
emission lamp and, just for fun, decide to turn up the power. The color of the helium
lamp changes and you look through the spectroscope. The emission wavelengths
are different! Alarmed, you turn the power back down and the gas emits the original
wavelengths. Explain these observations, specifically with regard to the helium gas; in
other words, what happened to the helium? You may assume that you did not break
the gas discharge tube or lamp!
14. Sirius A has a much dimmer companion star called Sirius B. Through careful
measurements of changes to Sirius A’s luminosity, astronomers have measured the
binary stars’ period: 50 years (that is, each star orbits the other once every 50 years). By
using high resolution digital images, the semi-major axis of 20 AU for the orbits was
a3
determined. Using the equation: P 2 =
where the period is measured in years,
Mbinary
the semi-major axis is measured in AUs and the mass of the binary system is measured
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in solar masses, determine the total mass of Sirius A and B system in solar masses. Show
your calculation!