PH109 Exploring the Universe, Test#4, Spring 2006

Please indicate the best answer to the following questions using the answer sheet provided.

1. Most of the mass of a galaxy is a. contained in the massive O and B stars in the galaxy. b. contained in the H I regions of the galaxy. c. contained in the H II regions of the galaxy. d. contained in the dark matter of the galaxy.

2. For what type of object is the period-luminosity relation used for determining distances? a. Algol variables, b. Cepheids, c. Cataclysmic variables, d. 21 centimeter radiation.

3. 21 cm radiation is produced by which element? a. hydrogen, b. helium, c. carbon, d. iron

4. In what part of the spectrum can astronomers observe the 21 cm radiation? a) visible, b) infrared, c) radio, d) X-Ray

5. What is the name of the nearest large galaxy to our own a. Milky Way, b. Andromeda, c. Orion, d. Cygnus

6. The location of our Sun in the galaxy is approximately a) near the core, b) near the outer edge c) about 2/3 of the way out to the edge, d) not currently determined

7. The radio emission from radio galaxies and quasars is due to a) thermal emission, b) blackbody radiation, c) O and B stars, d) synchrotron radiation

8. What is hardest to explain about spiral arm structure a) that they ever existed in the first place, b) why galaxies only have two of them c) why they have sharp boundaries, d) how they maintain themselves

9. When Galaxies collide a) their stars collide to form larger stars, b) both galaxies crumple into very dense systems c) they simply perturb each other’s shape, d) no galaxies are left after the collision

10. Why is the energy source of active galaxies thought to be extremely compact? a) Their energy is totally no stellar in origin. b) Their spectra are like those produced by ordinary stars. c) They vary on rapid time scales. d) They can be seen clearly; we can see that the energy source is compact.

11. Quasars were originally discovered as a) strong radio sources identified with star-like images on photographs b) variable sources of light c) bright galaxies, and only later found to be radio sources d) the only type of radio source within our galaxy

12. Why do the cores of spiral galaxies appear redder than the arms a) because of reddening due to dust, b) because the cores are older b) because the cores are further away, d) because of black holes in the center

13. Hubble’s law describes a relationship between a galaxy’s a) size and brightness, b) number of stars and size, c) shape and age, d) redshift velocity and distance 14. A rotation curve for a galaxy is a plot of a) orbital speed versus distance from center, b) number of rotations versus time c) orbital distance versus eccentricity, d) temperature versus luminosity

15. Which of these objects are not found in the Galactic Halo? a) RR Lyrae variables ,b) globular clusters,c) emission nebulae ,d) stars with comet-like orbits

16. The nearest comparable galaxy to our own is the a) Andromeda galaxy, b) Alpha Centari galaxy, b) Coma galaxy, c) Magellanic galaxy

17. Where are globular clusters located in the galaxy? a) in the nucleus, b) in the disk, c) in the spiral arms, d) in the halo

18. Irregular galaxies have ill defined shape because a) they rotate too slow to form a disk, b) active star formation disrupts disk c) too many black holes distort space time, d) recent collisions caused loss of shape

19. How do we know that the quasars are at large distances? a) they are extremely dim, b) they have large redshifts, c) they have large parallaxes, d) they are greatly obscured by interstellar dust

20. A tight, spherical collection of as many as several hundred thousand stars is a a) Galaxy, b) globular cluster, c) open cluster, d) Einstein's cluster

21. An Einstein ring is a a) group of galaxies which forms a ring in inter-galactic space b) something Al gave to his mother c) the theory that says the universe is a continuous ring of space time d) distortion of an image due to gravitational effects

22. Why don’t we see quasars in our local neighborhood? a) most quasars happened a long time ago so they are distant b) there is no room for quasars in our local neighborhood c) we must wait for their light to e red shifted first d) the gas and dust from out own galaxy keeps us from seeing them

23. What theory explains the formation of spiral arms: a) Hubble’s theory, b) Shapely’s theory, c) density wave theory, d) tidal wave theory

24. The size of our galaxy is about a) 3 light years, b) 120 thousand light years, c) one mega parsec, d) unknown at the present

25. If a galaxy is determined to be 2 million light years away, what does that mean a) it takes light 2 million years to cross the galaxy b) stars did not turn on till about 2 million years ago c) it takes light 2 million years to reach us from the galaxy d) if we could put our galaxy 2 million light years away it would look as bright as that galaxy.

26. Which of the following is not used to measure distances to the galaxies a) cluster H-R diagrams, b) novas, c) cepheid variables, d) parallax

27. About how long does it take for the Sun to complete one trip around the galaxy? a) 25 thousand years, b) 2.5 million years, c) 250 million years, d) 25 billion years

28. We cannot see the other side of the galaxy primarily because our view is blocked by a) too many stars, b) interstellar gas and dust, c) it is too far away, d) planetary nebulae 29. Which of the following is not a characteristic of the stars of the disk component of our galaxy? a. circular orbits, b. randomly inclined orbits, c. higher metal abundance, d. young stars

30. What observation of the Galaxy suggests it is much larger than the halo and contains a large amount of matter not in the form of stars? a) The rotation curve, b) Motions of the globular clusters c) The shape of the spiral arms, d) Infrared observations of the center of the Galaxy

31. Why are quasars called “quasi-stellar”? a) Their spectra strongly resemble the spectra of stars. b) They are ordinary stars located at vast distances from Earth. c) They look like stars on photographs. d) Like the stars visible in our night sky, quasars reside within the boundaries of the Milky Way.

32. What type of galaxy is frequently found at the center of a rich cluster of galaxies? a) elliptical, b) spiral, c) barred spiral, d) irregular

33. It is unlikely that astronauts will ever pass through black holes because a) they do not really exist , b) they are too small to hold a person c) they cannot be found because they are black and cannot be seen, d) tidal forces would rip them apart

34. Galaxies which show no structural features, but a smooth apparently three-dimensional luminosity, are called a) boring, b) spirals, c) irregulars, d) ellipticals

35. What is the most likely source of energy for active galaxies and quasars? a) Large clusters of very massive, luminous stars. b) A single supermassive, superluminous star. c) Accretion onto a supermassive black hole. d) Numerous supernovae from rapid star formation in young galaxies.

36. We can best see the spiral structure of our own galaxy by looking in the in which part of the spectrum? a) infrared, b) visible, c) radio, d) x-ray

37. What kind of galaxy do we live in? a) Spiral, b) elliptical, c) spherical, d) irregular

38. The very rapid orbital speed detected near the center of our galaxy suggests that a) our galaxy has a lot of stored angular momentum, b) massive stars are at the center c) a black hole is at the center, d) we have been in a collision in the past

39. The distribution of galaxies in the universe a) follows the same distribution as stars, b) arraigned on the surfaces of giant bubbles or voids c) fairly uniform, d) has remained the same as it was during the big bang

40. The visual astronomer who cataloged nuisance nebulae was a) Galileo, b) Einstein, c) Messier, d) Hubble