Astronomy 100

Section 1, Fall 2007

Hour Exam 2

Form B Answers

1. Granulation in the solar "surface" is produced by
b) convection

2. The most second-most abundant element in the Sun is
d) helium

3. Sunspots are produced by
c) localized magnetic fields that block convection

4. What event on the Sun causes aurorae on Earth?
a) coronal mass ejections

5. The length of the solar sunspot cycle, excluding any changes in the directions of magnetic fields, is
c) 11 years

6. In the first step of the proton-proton chain, two
a) protons fuse to deuterium

7. Counting from NOW, how long does the Sun have left to it until its core hydrogen runs out (in billions of years)?
b) 5

8. What makes the Sun hot in its center (hot enough to run fusion)?
e) gravitational compression

9. A 4th magnitude star is how many times brighter than a 5th magnitude star?
a) 2.5

10. The parallax of a star is 0.001 seconds of arc. What is its distance?
d) 1000 pc

11. What spectrum principally characterizes a class M star?
a) molecules (principally titanium oxide)

12. The standard spectral sequence is a result of
a) different stellar temperatures

13. We know that supergiants are really larger than giants because supergiants
e) are brighter than giants that have the same temperatures

14. Of the classic spectral sequence (OBAFGKM), the most common dwarf stars are of class
b) M

15. Stellar masses are found from
b) double stars

16. As you move up the main sequence from class M, stellar masses
c) increase

17. Below what stellar mass does the full proton-proton chain cease and a "star" is called a "brown dwarf?"
c) 0.08

18. You can determine the age of a star cluster by
d) the maximum mass of its main sequence stars

19. Which kind of main sequence star below will live the longest
period of time?
e) M

20. Open clusters are
d) all of the above: found in the Galaxy's disk; much less massive than globular clusters; are much more common than globular clusters

21. We know the age of the Earth and Moon to be about 4.5 billion years old from
b) the decays of radioactive elements

22. Earthquakes are caused by
b) crustal plates moving against each other

23. The Moon has
d) neither oceans nor any significant atmosphere

24. The large dark markings on the Moon are made of
e) solidified lava

25. The Earth's core is made mostly of
a) iron

26. The Earth's magnetic field is produced by the circulation of its
a) fluid core

27. Continental drift is caused by
e) convection in the Earth's mantle

28. Global warming and the greenhouse effect are at least in part caused by atmospheric
c) carbon dioxide

29. The Moon is thought to have been
c) born in a gigantic collision between Earth and a competing planet

30. Venus is hot primarily because of
b) its thick carbon dioxide atmosphere

31. Mercury is known for its
d) relatively huge iron core

32. In what way is Mars similar to the Earth?
a) polar caps, seasons, and rotation period

33. Evidence that a thick atmosphere once surrounded Mars comes from
a) old river beds

34. Mars's volcanos have grown large because
d) there is no plate motion

35. The visible clouds of Saturn are made of
a) ammonia

36. Jupiter is made mostly of
c) liquid molecular hydrogen

37. Saturn's satellite Titan is known for its
d) thick atmosphere and methane lakes/seas

38. If Saturn has only a third the mass of Jupiter, why is it almost as large?
e) The density is much lower as a result of lesser self-gravity

39. Saturn's rings are made of
d) ice coated rocks a few centimeters in diameter

40. Neptune has "captured" Pluto and
e) Triton

41. The least massive planet in the Solar System (barring Pluto) is
e) Mercury

42. The Sun's diameter is roughly
a) 10 times that of Jupiter, 100 times that of Earth

43. The asteroids are mostly found between
b) Mars and Jupiter

44. Pluto's status as a planet is controversial, as it is also a member of the
e) Kuiper Belt

45. Almost all meteors come from
b) comets

46. Metallic asteroids and metallic meteorites are made mostly of
e) iron

47. Comets have two tails, one made of an ionic gas, the other of
b) dust

48. Where do long-period comets come from?
b) the Oort Cloud

49. The inner planets have few volatile elements and compounds (like water) because
a) these planets formed close to the Sun and were hot

50. The planets all began to form through the accumulation of
c) dust grains in the solar nebula