Download Sample final exam

Astronomy 115
Sample final exam (comprehensive)
Open book, exercises, projects and notes, no collaboration. You have two hours
for this 100-point test.
Short answer: Answer all questions
1. The Sun was located in the constellation Taurus back at the beginning of the
quarter. Today, the Sun will be located in (choose one):
a. Taurus
b. Leo
c. Capricorn
d. Cancer
Tomorrow, the Sun will be located in (choose one):
a. the same constellation
b. the next constellation in the Zodiac order
c. the previous constellation in Zodiac order
d. off the Zodiac
2. Jupiter is moving in a retrograde fashion currently (until January), which
means it is moving (choose one):
a. west
b. east
c. some other direction
across the sky. This is good evidence for (choose one):
a. geocentrism
b. heliocentrism
c. magic
3. Two light bulbs of the same wattage are placed such that one is four times as
far away as the other. The ratio of brightness of the near bulb to the far bulb is
(choose one):
a. 1/16
b. ¼
c. 1
d. 4
e. 16
4. Matching: Match the observation (A, B C) with the correct conclusion (a, b, c)
A. Supernovae type Ia were dimmer in distant galaxies than expected
B. Normal stars near a radio source called Sagittarius A* have elliptical fast orbits
C. No matter where you look, the sky is filled with microwaves of a particular
frequency
a. Supermassive black hole at the center of the Milky Way
b. Evidence for the Big Bang
c. The universe is accelerating its expansion
5. More matching: Match the class of star with the largest nuclei it will create
through fusion during its main sequence phase.
O
helium
G
carbon
M
iron
6. Which of the following is produced by the proton-proton cycle in the Sun?
Choose all that are correct; not all the actual products are shown.
protons
electrons
helium nuclei
carbon nuclei
neutrons
neutrinos
oxygen nuclei
7. What is the overall color of a very young star cluster? Choose one.
Blue-white
Yellow
Orange
Red
8. The bright star Sirius is a main sequence star; it is currently
luminosity class _____ , but when it reaches the end of its hydrogen fusion
phase, it will become luminosity class ______ .
9. The graph to the left is (choose
one):
a. A Hertzsprung-Russell (H-R)
diagram
b. A Cepheid variable magnitudedistance diagram
c. The Hubble Law
d. An illustration of Einstein’s
special theory of relativity.
10. In the space within 20 ly of the Sun, there are few (choose one):
OBA class stars
G or K class stars
M class stars
dwarf stars
11. Meteorites made of nearly pure iron and nickel originally came from (choose
one):
a. a comet
b. an asteroid that underwent differentiation
c. an asteroid that did not differentiate
d. the core of the Earth
12. Match the equation with its appropriate use:
I =
λmax =
€
k
d2
The distance to a nearby star
2, 900, 000
T
The wavelength emitted by a glowing body
1
p
The method of standard candles
€
d =
€
13. The element that Earth-like life is most likely to use to build complex
molecules is (choose one):
a. hydrogen
b. carbon
c. silicon
d. iron
This element is the basis of life because (choose one):
a. it is incredibly common in the inner solar system.
b. it is relatively inert.
c. it is the oldest element in the universe.
d. it bonds to itself and other atoms equally well.
Philosophy section
14. The Drake equation (homework 8) calculates the number of possible
extraterrestrial civilizations with whom humans could communicate. Suppose I
use it and calculate that there are 180,000 possible civilizations with whom we
could communicate. Is my proposition a valid scientific theory? Recall that
“scientific” means that it must be justifiably quantitative, testable and
repeatable.
Graph section
15. Draw the Hertzsprung-Russell (H-R) diagram below, showing:
• labels and units for both axes
• the position of the Sun currently (should line up with marks on both axes)
• the path of the Sun’s evolution from protostar to main sequence star
• the path of the Sun’s evolution from main sequence star to its helium flash
Calculation section Choose one of the following problems; select the
appropriate equation, complete the calculation (show all steps) and answer any
follow-up questions for full credit. Hint: the equations necessary for this section
are on this exam somewhere.
16. The cosmic background radiation (CBR) is famously reported as 3 Kelvins.
But that’s a temperature, not a wavelength (as electromagnetic (EM) radiation is
usually reported). Calculate the wavelength of CBR in meters, and then
determine what part of the EM spectrum it is in. Recall that the
wavelength in the proper equation is given in nanometers (= 1 × 10–9 m).
17. Calculate the recessional velocity of the galaxy IC 4580, using either of the
calcium absorption lines. λref is 393.4 nm for the λ Ca K line and 396.9 nm for
the λ Ca H line; use c = 300,000 km/s. Then plot it on the wedge graph below.
Galaxy
name
IC 4580
RA
€
Dec
15 h 41
m6s
+28° 31’
Apparent
λ Ca K
magnitude line (Å)
15.4
4058
λ Ca H
line (Å)
4094
λ G-band
Fe (Å)
4441
18. Two binary stars, each with a mass of 0.5 solar masses, orbit each other.
Each has a semi-major axis of its orbit of 1.0 AU. What is the period (in years) of
these stars?
Essay section part one — Choose two of the following questions, and answer
them in paragraph style or with drawings, as the question states.
19. On page 184, the text states “Understand the fact that we [the Milky Way] are
moving toward M31 and that the Large Magellenic Cloud [LMC] is moving
toward us.” First, explain what we observe about these galaxies (M31, the
LMC) that shows they are moving in the directions the text states. I thought
motion was all relative; if the Milky Way is moving toward M31, then M31 is
moving toward the Milky Way. Second, explain how we infer if our galaxy is
moving or if the other galaxy is moving. Hint: M31 contains more stars than the
Milky Way, and the Milky Way contains more stars than the LMC.
20. Population I stars are those that lie on the disc portion of a galaxy; population
II stars are those that exist in the bulge of a galaxy (text, page 159). Population I
stars tend to be in classes O, B and A (not all of them are, fortunately). Population
II stars tend to be old red giants. First, given these two populations, what
differences in color would a galaxy have? Recall that the text (page 160) states
that there is “some evidence” that spiral galaxies evolve into elliptical galaxies.
Second, explain how the distribution of population I and II stars
supports this idea.
21. Electron degeneracy (page 134) is the reason given why white dwarf stars get
smaller (literally, a smaller radius) the more massive they get. This isn’t our
experience of normal matter; a gas, for instance, expands when there is more of
it, because otherwise the gas would increase its pressure. Draw two pictures,
one of normal matter, the other of degenerate matter, and show the forces acting
on the particles. The normal matter picture should show clearly why the matter
expands when there is more of it, and the degenerate matter picture should
show clearly why the matter shrinks when there is more of it.
Essay section part two — Choose two of the following and answer it in a
paragraph or so.
22. Carl Sagan famously said that we are all made out of “star stuff”. Let’s follow
that line of thought – assume you are made out of nothing but carbon,
hydrogen oxygen, nitrogen, sulfur (S) and phosphorus (P). Where was the
ultimate origin of all of the atoms of these elements that are now in your body?
Caution: they may have separate origins!
23. Classify the galaxy above, and state what color you would expect this galaxy
to be. To help with your classification, this galaxy emits more radiation, from
gamma rays to radio waves, than the Milky Way does. Explain why this type of
galaxy would be expected to emit such extra radiation.
24. Below are some characteristics of stars. Your task is to separate them into
two categories: the characteristics we can directly observe, and the characteristics
we must infer (in other words, figure out by models or equations). Write a
sentence for each to explain either what instrument is used to measure it or how
we use another number to infer this characteristic.
• apparent brightness
• spectral type
• radius
• mass