# Astronomy 10 - Summer 2000, Session A Final Exam - June 29th, 2000

Name:

Student ID #:

CLOSED BOOK, CLOSED NOTES, CALCULATORS ALLOWED
Mark all answers on SCAN-TRON form. Use a #2 pencil. Completely fill in the appropriate bubble. Be sure to thoroughly erase all altered answers and stray marks!

All 40 multiple choice questions are worth 2 points each. Read each question carefully before answering. Mark the bubble corresponding to the single best answer.

The 4 short answer questions are worth 5 points each. Use the space provided to answer with no more than two paragraphs and diagrams where appropriate.

You have 110 minutes to complete the exam

Turn in this multi-page set of questions along with your SCAN-TRON form.

## Possibly useful information

 C = 2r A = r2 SA = 4r2 V = (4/3)r3 1.22/D P2 = 42/G(m1+m2)*a3 F = ma F = -Gm1m2/r2 KE = (1/2)mv2 PE = -GMm/r E = KE + PE vesc = (2GM/R)1/2 Mint = v2r/G = c E = hc/ = h z = /o = v/c peakT = 3x10-3m*K = T4 L = 4R2T4 dpc = 1/p(") m1a1 = m2a2 b = L/(4d2) L M4 E = mc2 v = Hod = /crit 1 radian = 57.3° = 206,265" c = 3x108m/s G = 6.67x10-11m3*kg-1*s-2 h = 6.63x10-34Joules*s, 1 Joule = 1 kg*m2/s2 = 5.67x10-8 W m-2 K-4

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# Multiple Choice

1. If you lived on the side of the Moon that faces Earth, then you would witness a 1st Quarter Earth when the Moon was in which phase?
1. 1st Quarter
2. Waxing Gibbeous
3. Full
4. 3rd Quarter
5. Waning Crescent

2. How many times does the Sun transit the meridian in one year?
1. 1
2. 360
3. 364
4. 365
5. 366

3. How many times does a star transit the meridian in one year?
1. 1
2. 360
3. 364
4. 365
5. 366

4. The gravitational force exerted on a small mass (m) by a large mass (M) is
1. greater than the force exerted on M by m.
2. equal to the force exerted on M by m.
3. less than the force exerted on M by m.
4. either greater or less than the force exerted on M by m depending on the distance between them.
5. independent of the distance of separation.

5. If two thermal emitters have the same size and temperature but are made of different materials, which of the following statements is TRUE?
1. One will give off more red light than the other.
2. One will look brighter than the other.
3. One will reflect more photons than the other.
4. The number of photons given off by each will be the same, but they will have a different energy distribution.
5. Kangaroos are marsupials indigenous to Australia.

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6. Which one of the following statements about orbits is FALSE?
1. The "constant" in Kepler's third law, as generalized by Newton, actually depends on the mass of the planet under consideration.
2. An object in a highly elliptical orbit around the Sun has its greatest speed when it is far from the Sun.
3. The mass of the Sun can be determined by measuring Earth's orbital period and its distance from the Sun.
4. A planet moving in a circular orbit with constant speed is accelerating.
5. The orbit of an object around the Sun is hyperbolic or parabolic, if the object is not gravitationally bound to the Sun.

7. What is the distance of a star whose trigonometric parallax angle is 0.1"?
1. 0.01 parsecs
2. 0.1 parsecs
3. 1 parsec
4. 10 parsecs
5. 100 parsecs

8. If two stars have the same luminosity at visual wavelengths, but star Wayne is 3 times farther away from us than star Garth, then at visual wavelengths Wayne will appear
1. 3 times brighter than Garth
2. the same brightness as Garth
3. 1/3 the brightness of Garth
4. 1/9 the brightness of Garth
5. 1/81 the brightness of Garth

9. A star spends the bulk of its active lifetime as
1. a protostar
2. a main sequence star
3. a post-main sequence subgiant star
4. a red giant
5. a Cepheid variable

10. A main-sequence B-type star would be, with respect to our sun,
1. hotter and more red
2. hotter and more blue
3. cooler and more red
4. cooler and more blue
5. about the same since all main sequence stars are virtually alike

11. During its lifetime on the main sequence, a star tends to
1. shrink in size.
2. expand in size.
3. stay about the same size.
4. oscillate in size.
5. prefer the Beatles to Elvis.

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12. Star Pepito has transformed from the main sequence into a Red Giant. Its size has increased by 9 times and its surface temperature has dropped to 2/3 of what it was. How much more luminous is the star now?
1. The same as before
2. 4 times
3. 6 times
4. 16 times
5. 54 times

13. A solar mass white dwarf would be about the size of
1. Venus' orbit around the Sun.
2. the Sun itself.
3. Earth.
4. Manhattan.
5. a goat.

14. Which of the following statements is TRUE?
1. In 15 billion or so years there will be no remaining trace of the Sun because the planetary nebula thrown off by the Sun will have long since diffused into the interstellar medium.
2. In 15 billion years the most likely remaining artifact of the Sun will be a cold white dwarf.
3. The Sun will certainly undergo a Type II supernova.
4. The Sun will certainly undergo a Type I supernova.
5. The Sun will certainly undergo a series of nova events.

15. A massive star supernova can occur when
1. matter accreted from a nearby companion ignites on the surface of a white dwarf.
2. matter accreted from a nearby companion pushes the mass of a white dwarf over 1.4 solar masses, causing collapse and then explosion.
3. the iron core of a star rapidly collapses to form a neutron star which then rebounds, blowing off the outer layers.
4. the helium flash triggers rapid burning in the outer layers of the star.
5. someone goes to a Mexican restaurant and eats too many refried beans.

16. A white dwarf supernova can occur when
1. matter accreted from a nearby companion ignites on the surface of a white dwarf.
2. matter accreted from a nearby companion pushes the mass of a white dwarf over 1.4 solar masses, causing collapse and then explosion.
3. the iron core of a star rapidly collapses to form a neutron star which then rebounds, blowing off the outer layers.
4. the helium flash triggers rapid burning in the outer layers of the star.
5. hydrogen in the shell burns too rapidly.

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17. A massive star supernova could leave behind
1. a planetary nebula.
2. a neutron star.
3. a white dwarf.
4. a carbon core.
5. a magnesium core.

18. Which of the following statements about pulsars is FALSE?
1. The "pulses" emitted by a pulsar are believed to be produced when a beam of radiation from a rapidly rotating neutron star points toward our line of sight.
2. Pulsars were initially thought to be communication signals from intelligent extraterrestrials.
3. Pulsars are believed to have very strong magnetic fields.
4. A certain binary pulsar has provided the best existing evidence in support of Einstein's General Theory of Relativity.
5. Every neutron star should be detectable as a pulsar, if it is sufficiently close to us.

19. Interstellar dust does NOT
1. block light from background stars.
2. redden light from background stars.
3. scatter and reflect light from nearby stars.
4. emit light at characteristic wavelengths.
5. make distant stars appear closer.

20. In which of the following would you expect the greatest star formation rate at the present time?
1. The halo of a spiral galaxy.
2. The arms of a spiral galaxy.
3. The bulge of a spiral galaxy.
4. A globular star cluster.
5. An elliptical galaxy.

21. Globular clusters
1. are mainly located in the halo of the Galaxy.
2. are mainly located in the bulge of the Galaxy.
3. contain many hot, young stars.
4. are good places to look for massive star supernovae.
5. are asymmetrically distributed throughout the Galaxy.

22. Spiral arms can be maintained over long periods of time in our Galaxy because.
1. they are actually waves of compression that travel through the Galaxy, rather than material spiral arms.
2. they are caused by differential rotation in the Galaxy.
3. all stars in our Galaxy have the same period of rotation.
4. they consist entirely of lower main sequence stars, which have long lifetimes.
5. they get a lot of funding from the federal government.

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23. Most of the mass in the Milky Way Galaxy comes from
1. stars.
2. interstellar dust.
3. interstellar gas.
4. nougat.
5. unknown sources.

24. Proof that other galaxies existed was obtained by
1. using Cepheid variables in "spiral nebulae".
2. measuring the rotational motion of "spiral nebulae".
3. measuring the redshifts of "spiral nebulae".
4. measuring the distribution of globular clusters in "spiral nebulae".
5. examining the H-R diagram for stars contained in "spiral nebulae".

25. Which of the following things do Astronomers think lies in the nucleus of the Milky Way Galaxy?
1. an open cluster
2. a globular cluster
3. a magellanic irregular galaxy
4. a supermassive black hole
5. Jimmy Hoffa

26. Which of the following is NOT true about interactions between galaxies?
1. Astronomers have observed several galaxies that appear to be in the process of merging.
2. Giant elliptical galaxies in the centers of clusters probably got large by assimilating their neighbors.
3. Colliding gas during a galactic merger can trigger star formation.
4. Close encounters with other galaxies can tidally disrupt a galaxy's shape.
5. Stars often collide during galactic mergers.

27. The phenomena of AGN, Radio Galaxies, QSOs, and Quasars are thought to be
1. millions of supernovae all going off in a chain reaction at the centers of galaxies.
2. accretion disks around supermassive black holes seen in different projections and at different times.
3. white holes, the other end of a black hole where all the material that went in comes out.
4. regions in the Universe where matter and antimatter is mixing and annihilating.
5. completely different phenomena that have nothing to do with one another.

28. Most astronomers think that Olbers' Paradox, the darkness of the night sky, is resolved by the fact that
1. the Universe has a finite (rather than infinite) size.
2. the Universe has a finite age.
3. galaxies are distributed more homogeneously close by than they are far away.
4. there is obscuring dust that blocks out the light of the far away stars.
5. there is a vast government conspiracy to cover up the truth that alien beings are throwing a huge "blanket" over the Earth at night to block out the light of the Universe. The stars are really just lights that shine through the holes in the "blanket".

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29. If an absorption line of calcium is normally found at about 400 nm in a laboratory gas, and you see it at 440 nm in a spectrum of a galaxy, what is the approximate distance to the galaxy? (Assume that Hubble's constant is 50 km/s/Mpc.)
1. 600 Mpc
2. 2000 light years
3. 6 Mpc
4. 6 million light years
5. 6000 Mpc

30. Which of the following would NOT be a valid application of Hubble's Law?
1. Inferring the distance of the Large Magellanic Cloud, a satellite galaxy gravitationally bound to the Milky Way Galaxy, from the LMC's redshift.
2. Inferring the distance to a distant cluster of galaxies using its redshift.
3. Inferring the distance to a quasar by using its redshift.
4. Roughly estimating the age of the Universe from Hubble's law and the equation d = vt.
5. Inferring Hubble's constant from a distant supernova explosion of known luminosity, measured brightness, and measured redshift.

31. In maps of the large scale structure of the Universe what does the galaxy distribution look like?
1. A smooth and featureless distribution.
2. Voids, filaments, and sheets of galaxies.
3. Giant spherical shells of galaxies.
4. Large amorphous clouds of galaxies.
5. Arrows pointing to Disneyland.

32. Which of the following has NOT been used to infer the presence of dark matter?
1. Orbital speeds of stars and gas in galaxies.
2. The growth of large scale structure in the Universe.
3. Velocities of galaxies in clusters.
4. Gravitational lensing in rich galaxy clusters.
5. Orbital speeds of planets around the Sun.

33. Which of the following statements about the cosmic microwave background is FALSE?
1. It originates from the time when the Universe became transparent to radiation.
2. It now has a temperature of about 2.7 K.
3. Fluctuations in the radiation have been observed that could have grown into the large scale structure of the Universe observed today.
4. We cannot see anything beyond it.
5. It is explainable within the Steady State Theory of the Universe.

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34. If the average mass density of the Universe is less than the critical density and there is no Cosmological Constant.
1. The Universe is negatively curved and will expand forever.
2. The Universe is flat and will stop expanding at time equal to infinity.
3. The Universe is positively curved and will stop expanding and re-contract in what is called the Big Crunch.
4. The Universe is the interior of a black hole.
5. The Universe will stop expanding and become static.

35. In a positively curved, closed Universe
1. the interior angles of a triangle add to less than 180°.
2. there is a definite edge.
3. the volume is infinite.
4. parallel lines always meet.
5. people actually like Kathie Lee Gifford.

36. The center of the Universe
1. is the Earth.
2. is the Sun.
3. is a point 8 kpc from the Sun on which the globular clusters are centered.
4. does not exist within our Universe.
5. is 42nd and Broadway, New York City.

37. Which of the following is most likely the correct sequence in the Universe's history.
1. big bang, helium forms, the Universe becomes transparent to radiation, the first stars, us.
2. big bang, helium forms, antiparticles exists in equilibrium, the Universe becomes transparent to radiation, us.
3. antiparticles exist in equilibrium, helium forms, the Universe becomes transparent to radiation, us, the first stars.
4. big bang, helium forms, the first stars, the Universe becomes transparent to radiation, us.
5. big bang, the Universe becomes transparent to radiation, antiparticles exist in equilibrium, the first stars, us.

38. A flashlight is moving toward you at 1/2 the speed of light. What speed do you measure for the incoming photons?
1. 3/2 c
2. 1/2 c
3. (1/2)1/2 c
4. (2)1/2 c
5. c

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39. As Bob sees Jill approach the speed of light relative to him, he will see
1. her mass decrease.
2. time moving more quickly for her.
3. the length of her spacecraft and everything within becoming shorter in the direction of relative motion.
4. an increase in his own mass.
5. her horrible future in which she becomes stranded on a planet of damn dirty apes.

40. Bob is traveling in a spaceship toward a 1 solar-mass black hole. Jill is watching from a safe distance away. Which of the following statements is FALSE?
1. Jill will see tidal forces rip Bob's spaceship apart.
2. Jill will see Bob get closer and closer to the event horizon, but she will not see him cross it until the time (measured by her watch) becomes infinite.
3. Bob's spaceship will appear to get redder as it approaches the black hole.
4. Jill will see Bob squished into a mathematical point (a singularity).
5. Jill will see Bob's watch tick more and more slowly as he aproaches the black hole.

1. Describe Nicolas Copernicus' accomplishment which began what came to be known as the Copernican Revolution. How was this revolution later continued by Harlow Shapley and then Edwin Hubble?

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2. Draw an H-R diagram for a 10 billion year old cluster. Indicate the main sequence, main sequence turn-off, red giant branch, and white dwarfs. Be sure to label your axes.

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3. Draw a diagram that illustrates the simple geometrical situation of a gravitational lens.
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4. Carl Sagan was fond of saying that "we are starstuff". What did he mean by that?
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