PH109 Exploring the Universe, Test #4, Fall, 1998

NAME______

Please indicate the best answer to the following question on the answer sheet provided. All questions are worth 2 points unless noted otherwise.

1. What perception of the Milky Way Galaxy did astronomers have in the early part of this century? a) They believed that the Earth rested inside concentric spheres, with the Milky Way stars fixed to the outermost sphere. b) They believed that the Milky Way was one of billions of galaxies in the universe. c) They believed that the Milky Way was the entire universe. d) They believed that, because the Sun was at the center of the Milky Way, it was impossible to see the rest of the universe.

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

3. The location of the center of the Galaxy is determined by observations of: a) Cepheids. b) Globular clusters. c) The spiral arms. d) A visually bright, massive, object around which all objects in the Galaxy move.

4. From the Sun, what is the distance to the Galaxy's center? a) 8 kpc, b) 30 kpc, c) 300 pc, d) 1000 Ly.

5. Which is the correct description of the Sun's location within the Milky Way? a) At the outer edge of the galactic bulge but in the plane of the disc. b) In the disc but at its outer edge. c) Above the disc and about one-third of the galactic radius from the center. d) In the disc and about one-half a galactic radius from the center.

6. What two observations of an object allow for a determination of the Milky Way's mass? a) Object's mass and velocity. b) Object's age and distance from the galactic center. c) Object's mass and age. d) Object's velocity and distance from the galactic center.

7. Which of the following is not found in the Galaxy's halo? a) globular clusters b) old stars c) stars with random, three dimensional orbits d) red stars e) emission nebulae

8. Which of the following is not found in the Galaxy's spiral arms? a) young star clusters, b) O and B stars, c) globular clusters, d) emission nebulae

9. The object located at the center of the Galaxy is believed to be a ______. a) a large cluster of stars, b) an enormous emission nebula c) a black hole, d) a massive supernova 10. What property is common to all spiral galaxies? a) Ongoing star formation., b) The disk, the bulge, the halo, and the corona. c) Abundant interstellar gas, d) all of the above

11. The Magellanic Clouds are known for certain as: a) Small irregular galaxies that move in orbit around our Milky Way. b) Regions of active star formation in the outer halo of the Milky Way. c) Hazy patches of nebulae visible from Earth's Northern Hemisphere. d) Dark clouds of dust that are known regions of star formation.

12. Why does the Cepheid distance technique have limited usefulness beyond 5 Mpc? a) Distant galaxies are seen in the past, when Cepheid variables behaved differently than they do today. b) Distant galaxies are so young they do not contain Cepheids. c) Cepheids are too faint to be seen. d) The light variability of Cepheids diminishes with distance so that at 5 Mpc they do not appear to vary.

13. Collisions between galaxies: a) Turn ellipticals into spirals, b) May cause bursts of star formation. c) Cause large numbers of stars to collide and explode, d) Never occur.

14. What is the Great Wall? a) It is not a structure but a distance beyond which astronomers cannot view galaxies. b) It is the time before the universe started expanding; a time about which we can never know anything. c) It is a large sheet of galaxies measuring 70 Mpc by 200 Mpc. d) It is an enormous intergalactic cloud of dust and gas that hides more distant galaxies.

15. Which of the following is the Hubble Law? a) The greater the distance to a galaxy, the greater its redshift. b) The greater the distance to a galaxy, the fainter it is. c) The more distant a galaxy is, the younger it appears. d) Most galaxies belong to a cluster; most clusters are part of a super cluster.

16. What does the Hubble Law measure? a) The rate of expansion of the universe. b) How galaxies are distributed in the universe. c) How light gets fainter with increasing distance. d) Light travels at a finite speed; we see objects the way they were when the light left them, not the way they are when we make our observation.

17. A galaxy is at a distance of one billion light years. Which of the following is true? a) We see the galaxy the way it will be in one billion years. b) We see the galaxy the way it was one billion years ago. c) We see the galaxy the way it was when the universe was one billion years old. d) We see what our galaxy will be like in one billion years.

18. In a lobe radio galaxy, the ultimate energy source for the entire galaxy is thought to reside: a) In the lobes, b) In the galaxy's center, c) In the jets, d) all of the above

19. 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. 20. The look-back time of an object is directly related to its: a) Distance, b) Variability, c) Luminosity, d) Size.

21. Why do some quasars have red shifts greater than 1? a) They are very distant. b) They are moving away from us faster than the speed of light. c) It is impossible to have a redshift greater than 1. d) They are moving towards us.

22. What was discovered about the spectra of quasars? a) The emission lines were from completely unknown elements. b) The emission lines were formed by completely new processes never before observed. c) They contained normal emission lines that were highly red shifted. d) For the first time, stars were discovered to have radio emission lines.

23. 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.

24. Synchrotron radiation produces a ______spectrum. a) continuous, b) emission, c) absorption, d) all of the above

25. Quasars have their distances measured by what technique? a) Cepheids, b) Supernovae, c) parallax, d) Hubble law

26. Which of the following is a description of the optical appearance of a quasar as seen through any telescope? a) large, glowing red cloud with a dark center b) a relatively small disc of light that is intensely blue c) they are invisible at optical wavelengths d) like a relatively faint star e) brightly glowing filaments of gas, rapidly expanding outward

27. William Herschel made his galactic map by a) measuring the red shifts of nearby stars b) using radio astronomy techniques c ) counting stars in all directions. d) computer modeling

28. Pulsating variables a) are useful for determining distances, b) are useful for determining masses c) are useful for determining the age of the galaxy, d) are useful for explaining pulsars

29. It has been established that there is a ______at the center of the Galaxy. a) black hole, b) QUASAR, c) HII region, d) super massive star formation

30. Why is our galaxy in the shape of a disk a) because it rotates b) because it got sheered off during a galactic collision c) the outer parts were torn away by the Magallenic clouds d) the dark matter holds it in that formation

31. How long does it takes the Sun to travel around the center of the Galaxy a) one billion years, b) 250 million years, c) one million years, d) 5 billion years 32. Globular clusters are located in the ______region of our galaxy. a) outer, b) spiral arms, c) halo, d) near the black hole

33. The distribution of spiral arms in the Galaxy has been determined from observations of a) the 21 cm radiation, b) star formation, c) infrared radiation, d) Hubble's Law

34. We can estimate the mass of the Galaxy by a) counting how many stars we see, b) using P2 = a3 c) comparing it to other galaxies we can see d) measuring the local curvature of space-time

35. The Milky Way is an example of a ______galaxy. a) spiral, b) elliptical, c) captive, d) isolated

36. The discovery of ______in the Andromeda Galaxy by Hubble finally allowed its distance to be measured. a) black hole, b) red shifted spectral lines, c) planets, d) stars, e) super novae

37. Because the mass of the Galaxy continues to increase significantly with distance from its center, astronomers now believe there is a) other galaxies perturbing our orbit, b) many black holes throughout space c) dark mater, d) a modification to Newton's law of gravity

38. The two dwarf irregular companions of the Milky Way Galaxy are known as the a) bi-polar nebular, c) M31 and M32, d) Happy and Sleepy, e) large and small Magellanic clouds

39. Galaxies which show no flat structural feature, but just a smooth apparently three-dimensional luminosity structure, are called a) boring, b) spirals, c) irregulars, d) ellipticals

40. When galaxies collide, a) individual stars collide, b) millions of stars form into black holes c) only the spiral arms collide, d) they pass right through each other 41. (10 points) Explain the differences between spiral, irregular, and elliptical galaxies.

42. (10 points) Define the following parts of a spiral galaxy: a) core, b) halo, c) disk, d) spiral arms