PH109 Exploring he Universe, Test #3, Fall, 1998
Name______
Indicated thebest answer to the following questions on the answer sheet provided. All questions are worth two points unless stated otherwise.
1. Magnetic fields inside sunspots are ______those in surrounding regions.
a) much stronger than, b) slightly stronger than, c) the same as, d) much weaker than
2. Why couldn't you stand on the Sun's surface?
a) You could stand on the surface.
b) The Sun doesn't have a solid surface.
c) The Sun's surface is too highly magnetized for anything to survive there.
d) You could stand on it, if a sufficiently protective spacesuit could be designed.
3. The temperature of the layer of gas that produces the visible light of
the Sun is about ______.
a) 15 million K, b) 300,000 K, c) 10 million K, d) 1 million K, e) 5800 K
4. What is the net result of the proton-proton chain?
a) 2 heliums are fused into 1 carbon, 1 neutrinos + energy
b) 4 hydrogens are fused into 1 helium, 2 neutrinos + energy
c) 2 hydrogens and 1 helium are fused into 1 carbon + energy
d) 2 protons and 2 neutrons are fused into 1 carbon + energy
5. What star has the largest proper motion?
a) The Sun, b) Proxima Centauri, c) Barnard's Star, d) None of the above.
6. Which of the following apparent magnitudes is the brightest?
a) 5.0, b) 15.8, c) 3.2, d) -1.1
7. Which of the following spectral types is the hottest?
a) G2., b) A5., c) K9., d) O2.
8. Which of the following is the most common type of star?
a) White dwarfs., b) Red giants., c) Main Sequence., d) Supergiants.
9. What is the single most important characteristic in determining the course of a star's evolution?
a) Absolute brightness., b) Distance., c) Surface temperature., d) Mass.
10. What characteristic of the stars in a binary system can be determined by knowing the period of the stars' common orbit and the distance between them?
a) Absolute brightness., b) Sizes of the stars., c) Surface temperature., d) Mass.
11. Why are star clusters almost ideal "laboratories" for stellar studies?
a) The combined light of the stars makes them easier to see.
b) Like our Sun, stars in clusters are always located in the plane of the Milky Way Galaxy.
c) Stars in clusters have the same age, similar composition, and lie at approximately the same distance away.
d) Stars in clusters are all relatively young and therefore shine brightly.
12. What physical property of a star does the spectral type measure?
a) luminosity, b) temperature, c) radius, d) mass, e) composition
13. In the HR diagram, what is the approximate position of the Sun?
a) bottom left, b) top right, c) top left, d) bottom right, e) center
14. Interstellar gas is composed mainly of:
a) Hydrogen and helium.
b) Carbon.
c) Ammonia, methane, and water vapor.
d) Hydrogen and carbon.
15. Why is 21-cm radiation so important to the study of interstellar matter and the Galaxy?
a) Emitted by hydrogen, it passes through interstellar dust and allows us to see the entire Galaxy.
b) Emitted by carbon monoxide, it passes through interstellar gas and allows us to see the entire Galaxy.
c) It is emitted by most stars, enabling astronomers to map the entire Galaxy.
d) It is emitted only in regions of star formation, so the pattern of the spiral arms of the Galaxy can be mapped.
16. Complex molecules in interstellar space are found:
a) Inside dense dust clouds.
b) Scattered evenly throughout space.
c) Only around supergiant stars.
d) Surrounding low luminosity main sequence stars.
17. Most stars probably formed:
a) Alone., b) In clusters., c) From constellations., d) In the nucleus of the Galaxy.
18. What happens when an interstellar cloud fragment shrinks?
a) Density rises., b) Temperature rises., c) Pressure increases., d) all of the above, e) none of the above
19. Which event marks the birth of a star?
a) Fusion of hydrogen atoms into helium atoms.
b) Collapse of an interstellar cloud.
c) Formation of a photosphere.
d) Instability in an interstellar cloud.
20. The final core element for a massive star is
a) carbon, b) oxygen, c) silicon, d) iron
21. A high-mass star dies more violently than a low-mass star because:
a) It generates more heat and its core eventually collapses.
b) It cannot fuse elements heavier than carbon.
c) Gravity is weakened by its high luminosity.
d) It is most often found as part of a binary system.
22. What is a planetary nebula?
a) A planet surrounded by a glowing shell of gas.
b) The disc of gas and dust surrounding a young star that will soon form a solar system.
c) The ejected envelope of a red giant surrounding a stellar core remnant.
d) A type of young, medium mass star.
23. Which of the following represents the last observed stage in the evolution of a low-mass star?
a) Red giant., b) Planetary nebula., c) Brown dwarf., d) White dwarf.
24. A star spends most of its life:
a) As a protostar.
b) In explosions lasting millions of years.
c) As a red giant or supergiant.
d) As a main sequence star.
25. What characteristic of a star cluster is used to determine its age?
a) The number of red giants.
b) The faintest stars seen in the cluster.
c) The main sequence turnoff.
d) The total number of stars in the cluster.
26. Astronomers talk about "low-mass" and "high-mass" stars with regard to their evolution. In units of solar masses, what is the dividing line, that is, the lowest mass for a high-mass star?
a) 2, b) 4, c) 8, d) 12, e) 20
27. What is the primary composition of a white dwarf?
a) hydrogen, b) helium, c) carbon, d) oxygen, e) silicon
28. What are black dwarfs?
a) the lowest mass main sequence stars
b) the end result of massive star evolution
c) objects that are not quite massive enough to be stars
d) cooled off white dwarfs
e) the objects at the centers of planetary nebulae
29. What is not the same for each star in a cluster?
a) age, b) mass, c) composition, d) distance from Earth
30. Nearly all the elements found in our environment were formed inside stars. The major exceptions are:
a) Iron and nickel., b) Oxygen and carbon., c) Silver and technetium., d) Hydrogen and helium.
31. A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object?
a) Nova., b) Type-I supernova., c) Type-II supernova., d) Contact binary.
32. An iron core cannot support a star because:
a) Iron has poor nuclear binding energy.
b) Iron cannot fuse with other nuclei to produce energy.
c) Iron supplies too much pressure.
d) Iron is in the form of a gas, not a solid, in the center of a star.
33. The heaviest nuclei of all are formed:
a) During a supernova explosion
b) During a nova explosion
c) During carbon burning
d) During all stages of stellar evolution of massive stars
34. A star can be a supernova:
a) Many times.
b) At various times, depending on the mass of the star.
c) Once.
d) Early in its evolution.
35. The supernova that formed the Crab Nebula was observed in what year?
a) A.D. 1054., b) A.D. 1987., c) 9000 B.C., d) A.D. 1604.
36. What compelling evidence links pulsars to neutron stars?
a) Both pulsars and neutron stars can be found in globular star clusters.
b) Only a small rotating source of radiation is thought to be able to emit precisely timed pulses such as those from pulsars.
c) Pulsars are known to evolve into neutron stars.
d) Both pulsars and neutron stars have been discovered near the Sun.
37. The observed slowing of a clock in the vicinity of a black hole is a prediction of:
a) Special relativity.
b) General relativity.
c) Stellar nucleosynthesis.
d) The Principle of Cosmic Censorship.
38. What explanation does general relativity provide for gravity?
a) Gravity is a result of curved spacetime.
b) Gravity is directly proportional to mass.
c) Gravity is inversely proportional to radius.
d) all of the above
e) none of the above
39. Which of the following are attracted by gravity?
a) any object with mass
b) electromagnetic radiation
c) neutrinos
d) all of the above
e) none of the above
40.Which affects occur when a person travels near the speed of light.
a) time runs slower
b) mass increases
c) length contracts
d) all of the above
e) none of the above
41. (10 points) Construct and label a HR diagram and show where the main sequence stars are located. Finally show where the Sun is located.
42. (10 points) Briefly describe the phases our Sun will go through starting on the main sequence and ending when the Sun is no longer visible.