## Practice Final Exam

#### Section I. TRUE--FALSE

1. A black hole will suck you in if you approach within its tidal (Roche) radius.

2. Reflection nebulae look blue because the dust in them scatters blue light from stars more than red light.

3. The interstellar medium is a hot, very diffuse gas in which colder clouds consisting mainly of atomic or molecular hydrogen are found.

4. The irregular lanes of darkness running through photographs of the Milky Way are places where stars have died out.

5. Globular clusters are part of the halo component of the Galaxy.

6. Population II stars have relatively small amounts of heavy elements because they are too young to have made them yet.

7. Open clusters are found in the Galactic disk and only contain Population I stars.

8. Galactic globular clusters do not appear uniformly distributed in all directions from the Earth.

9. The Cepheid variables are "standard candles" for measuring distances to nearby galaxies.

10. Shapley thought the spiral nebulae were located inside our solar system.

11. Some galaxies are observed by radio telescopes to be shooting two oppositely-directed jets of material millions of light years into intergalactic space.

12. The Hubble law can be applied to stars within our own galaxy if you correct for the effects of dust.

13. One scenario for the formation of some elliptical galaxies involves collisions between spiral galaxies.

14. Elliptical galaxies contain relatively little interstellar material and many cool red giants.

15. The cosmic background radiation is the nearly uniform background of light produced by distant redshifted stars in the observable part of the Universe.

16. Quasars are among the most luminous objects in the Universe.

17. Gravitational lenses are useful to astronomers because they allow us to measure the masses of distant quasars.

18. Supernovae in spiral galaxies occur only inbetween the spiral arms.

19. The luminous matter in the Universe has, by itself, insufficient gravity to cause the eventual collapse of the Universe.

20. During the early part of the Big Bang, it was so hot that photons could easily create proton/antiproton pairs out of energy.

21. The gravitational force exerted by a person on a black hole equals the gravitational force the black hole exerts on the person.

22. The first quarter moon rises approximately at noon and sets at midnight.

23. Different constellations are visible at night in Winter compared with Summer because of the orbital motion of the Earth around the Sun.

24. The moon is always full just before a solar eclipse.

25. High tide occurs exactly once every day, regardless of your location on the Earth.

26. The density of material in the Earth's core is higher than in the mantle because the heavier material sank to the center of the Earth.

27. The terrestrial planets must have formed before the gas giants because the gas giants used up all the remaining planetesimals.

28. An ideal blackbody emits radiation at a single frequency corresponding to its composition.

29. The spectra of gas clouds can sometimes show absorption lines and sometimes emission lines.

30. Light at visible wavelengths is scattered by dust less than at radio wavelengths.

31. Smaller parallax implies greater distances.

32. The fact that hot stars look blue and cool stars look red is a due to the fact they emit much like blackbodies.

33. All telescopes contain two lenses, the objective and the ocular.

34. The angular resolution of a telescope depends on the wavelength at which the telescope operates.

35. Because of the greater amount of fuel available to them, more massive stars have longer lifetimes.

36. The elements between oxygen and iron can be produced in the interiors of massive stars.

37. Our Sun's energy is mainly produced by the proton-proton chain.

38. The main source of energy for a white dwarf is the CNO cycle.

39. In a eclipsing binary system, when the smaller star is totally
eclispsed by the larger star, the light curve always reaches its minimum value.

40. Pre-main sequence and post-main sequence stars can both be found in the upper righthand part of the HR diagram.

41. By plotting all the stars in a cluster on an HR diagram, you can tell whether the cluster is an open cluster or globular cluster.

#### Section II. MULTIPLE CHOICE.  Choose the best answer.

42.  The distances of the MOST distant galaxies are measured by

\a  observing the pulsation periods of Cepheids in them
\b  assuming they have the same luminosity as local galaxies
\c  cosmological parallax
\d  measuring their redshift and using the Hubble law
\e  measuring their brightness and 21-cm spectral linewidths

43.  Hydrogen gas falls from a companion star onto the surface of a white dwarf until enough heat and pressure build up.  Then hydrogen fusion causes this accreted surface to be blown off the star.  This event is known as
\a a type I supernova.
\b a type II supernova.
\c the helium flash.
\d the hydrogen flash.
\e a nova.

44.  Which of the following is NOT a characteristic of star-forming regions?
\a there is a lot of CO gas found in the region
\b planetary nebulae are more common here
\c there are often HII regions in the vicinity
\d a Type II supernova has gone off recently
\e it is in the middle of a spiral arm

45.  Which of the following is NOT a structural element of the Milky Way Galaxy?

\a halo
\b nucleus
\c mantle
\d bulge
\e disk

46. Bulges are red / disks are blue / the reason for that / is given by you!

\a  young bright massive stars are generally in found in disks, not bulges
\b  interstellar reddening is stronger in bulges than disks
\c  blue light is scattered less by disks than bulges
\d  there are very few red giants in disks
\e  most star formation occurs in bulges rather than disks

47.  The rotation velocity of a spiral galaxy can be measured by observing

\a the expansion of space
\b the motion of the globular clusters
\c the number of turns in the spiral arms
\d the differential doppler shift of its 21-cm radiation
\e the size of the halo

48.  Radio astronomy is useful in studying galactic structure because

\a radio waves are caused by spiral density waves
\b dark matter only emits at radio wavelengths
\c most of the Galaxy is ionized and can only be seen by radio telescopes
\d dust clouds stand out at radio wavelengths because they are so cold
\e neutral hydrogen emits at 21-cm and can be detected across the Galaxy

49.
The massive black hole at the center of the Milky Way

\a is not surprising because black holes are common in the centers of spiral galaxies.
\b formed from the death of a roughly one million solar mass star.
\c is very bright in visible wavelength images.
\d is rapidly destroying all the stars in the bulge.
\e has jets of gas streaming out in several directions at nearly the speed of light.

50.  The recession velocity of a galaxy four hundred million ly away (using a Hubble constant of 25 km/s/$10^6$ly) is

\a  2.5$\times 10^6$ km/s
\b  nearly the speed of light
\c  5000 km/s
\d  1$\times 10^4$ km/s
\e  5$\times 10^5$ km/s

51.  Which of the following is FALSE about clusters of galaxies?

\a Galaxy clusters can gravitationally lens distant quasars.
\b Galaxy clusters provide evidence against the dark matter theory.
\c Galaxies within a cluster orbit the cluster center of mass.
\d Galaxy clusters can have a lot of X-ray emission from gas inbetween the galaxies.
\e Galaxy clusters can be gravitationally bound together to form
superclusters.

52.  The formation of galaxies is most analogous to which of the following processes?

\a black hole formation
\b star formation
\c the Big Bang
\d inflation
\e nucleosynthesis

53.  Supermassive black holes can be found in the center of

\a AGNs.
\b most spiral galaxies.
\c quasars.
\e all of the above.

54.  Distant quasars appear to be receding most quickly (of any observed objects) because

\a  they are the objects ejected most quickly during the Big Bang
\b  they are the brightest and therefore the fastest objects known
\c  they have the highest antimatter content and are repelled
\d  they are furthest from most of the matter in the Universe
\e  there is the most expanding space between us and them

55.  A member of the Rebel Alliance flies toward a black hole in pursuit of an evil fiend. She has blue running lights on the back of her ship.  Shortly before she reaches the event horizon, you notice that the photons from the lights

\a now appear red and faint.
\b are curving away from you.
\c are moving at less than the speed of light.
\d are coming at a higher and higher rate.
\e are turning back

56.  The microwave background contains photons that

\b  show the Universe when it was last opaque
\c  are emitted by evaporating black holes
\d  form the event horizon
\e  are piped into your microwave oven

57.  The mass--to--light ratio of galaxy clusters is 100 or more (in solar units). This implies:

\a  the total mass of dark matter is many times that of normal matter
\b  the typical cluster has 100 galaxies or more
\c  only about 1/100  of the light can escape a cluster of galaxies
\d  99% of the stars in clusters shine at 1% of a solar luminosity
\e  most stars in cluster galaxies are 100 times brighter than the Sun

58.  Which of the following was probably NOT a source of some atoms in your body.
\a  proton production from photons early in the Big Bang
\b  carbon fusion in the core of a brown dwarf
\c  triple alpha reactions in a red giant
\d  the blast wave from a Type II supernova
\e  the expanding shell of material in a planetary nebula

59.  Which of the following is NOT evidence for a creation event in the Universe only billions of years ago.
\a  a blackbody spectrum of microwave photons in all directions
\b  the Hubble expansion of the galaxies
\c  the age of the oldest globular clusters
\d  the flat rotation curves of spiral galaxies
\e  the fact the night sky is dark

60.  Which of the following has NOT been used as evidence for dark matter?

\a The orbital speeds of the planets in the solar system
\b The orbital speeds of stars in normal spiral galaxies
\c The orbital speeds of galaxies in binary pairs of galaxies
\d The orbital speeds of galaxies in large clusters
\e The gravitational lensing by rich clusters of galaxies

61.  Which of the following probably does NOT involve an accretion disk?

\a  the radio jet from an active galactic nucleus
\b  the formation of the solar system
\c  the rings around Saturn
\d  X-rays from galactic stellar black holes
\e  a classical nova

62.  The Earth's seasons are caused by

\a the Earth's elliptical orbit.
\b the fact that the Sun gets hotter and cooler throughout the year.
\c the tilt of the Earth's orbit with respect to the tilt of the Sun.
\d the tilt of the Earth's rotational axis with respect to its orbit.
\e the presence of the Moon.

63.  As viewed from a point on the surface of the Moon today, the Earth is directly overhead. From that same point, the Earth will set in

\a  never
\b  one month
\c  two weeks
\d  one day
\e  6 hours

64.  The most important reason that the surface of Venus is much hotter than that of the Earth is that

\a Venus is larger than the Earth.
\b the surface of Venus is much darker (i.e. absorbs more light) than the surface of the Earth.
\c the atmosphere of Venus contains much more carbon dioxide, creating a stronger greenhouse effect.
\d Venus is closer to the Sun than the Earth is.
\e Venus has no protective ozone layer to block ultraviolet radiation.

65.  Which of the following objects is youngest (formed most recently)?

\a the Moon
\b Saturn's rings
\c comets
\d the Sun
\e Io

66.  Which of the following has a composition most like that of the original protoplanetary disk?

\a  Earth
\b  meteors
\c  Jupiter
\d  asteroids
\e  planetesimals

67.  The corona of the Sun

\a  contains large sunspots
\b  heats the photosphere
\c  emits mostly X-rays
\d  lies beyond the solar wind
\e  all of the above

68.  You observe a 10 solar mass star in a binary system with a companion that does not give off enough light to be seen.  However, you do know that the binary's period is 20 years, and the semimajor axis is 20 AU.  What is the companion object?

\a it can't be determined from this information
\b a brown dwarf
\c a white dwarf
\d a neutron star
\e a black hole

69.  After Jabba freezes Han Solo in carbonite, Han's body temperature drops from its original 300 K down to 150 K.  What happens to the peak wavelength of Han's blackbody emission?

\a It increases by a factor of 2$^4$.
\b It increases by a factor of 4.
\c It increases by a factor of 2.
\d It decreases by a factor of 2.
\e It decreases by a factor of 2$^4$.

70.  To use trigonometric parallax to find the distance to a star, we must know

\a the Sun's diameter
\b the star's angular size
\c the distance from the Earth to the Sun
\d the star's spectral type
\e the velocity of the star

71.  Applying the Stephan-Boltzman law, you can conclude that a star which is very luminous but very small must be

\a  very faint
\b  very far away
\c  very red
\d  very hot
\e  very massive

72.  The most massive known star is about how many times more massive than the least massive star?

\a  10
\b  100
\c  1000
\d  10000
\e  100000

73.  During its lifetime on the main sequence, a star tends to

\a triple in size
\b shrink in half
\c double in size
\d stay about the same size
\e oscillate in size by a factor of two

74.  The Sun will eventually die and finally end up as a

\a quasar
\b protoplanetary nebula
\c red giant
\d neutron star
\e white dwarf

75.  A main sequence B-type star would, in comparison to our Sun,

\a be hotter and bluer
\b be cooler and redder
\c spend a longer time on the main sequence
\d be similar except for its chemical composition
\e be intrinsically less luminous

76.  The intrinsic luminosity of a star can be found if you know

\a its mass
\b whether or not its burning hydrogen
\c its composition
\d its radius and surface temperature
\e its apparent brightness

77.  Which of the following parameters is NOT needed in order to calculate the mass of an unseen planet orbiting a star by the Doppler technique (i.e. using Kepler's Law):

\a the distance from us to the star
\b the mass of the star
\c the period of the orbit
\d the inclination of the orbit
\e the velocity curve of the star

78.  A time-lapse photograph of the night sky taken at the South Pole will show the stars moving in ______, while one taken at the equator will show the stars moving in ______.

\a circles, circles
\b straight lines, straight lines in the same direction
\c straight lines, straight lines in the opposite direction
\d straight lines, circles
\e circles, straight lines

79.  If 2 objects have the same apparent brightness, but one is four times as far away as the other, the ratio of their intrinsic luminosities is:

\a 2:1
\b 4:1
\c 8:1
\d 16:1
\e 64:1

80.  Which of the following is NOT a good reason for believing life might be common in the Galaxy?

\a  on the Earth, life appeared soon after it was possible
\b  most stars in the Galaxy are in binary pairs
\c  protoplanetary disks are a common effect of star formation
\d  the elements needed for organic chemistry (H,C,N,O) are among the most common elements
\e  habitable zones are probably more diverse than the surface of the Earth