1. Night and day are caused by the rotation of the Earth.

2. Our closest neighboring large galaxy is the Andromeda galaxy, which is 2 million light years away. If a supernova explodes in the Andromeda galaxy, it will be 2,000,000 (2 million) years before we see this happen.

3. Lunar and solar eclipses do not happen every month because the Moon's orbit around the Earth is tilted compared to the Earth's orbit around the Sun.

4. When you see a star, light is emitted by the star and enters your eye.

5. As a glowing body gets hotter, it emits more photons, and these are typically more energetic.

6. If you push a ball with your hand (apply a force to it), the ball moves in the direction the force was applied, and your hand feels an equal force in the opposite direction.

7. An atom can absorb a photon of light if the energy of the photon equals the energy difference between electron orbits.

8. The gravitational force between two objects is larger between objects of larger masses, and decreases as the square of the distance between the objects.

9. The main reason it is hotter in the summer than in the winter is the Sun is up longer and is higher in the sky.

10. If you are in a completely dark room, with no lights and no windows, you can't see anything.

11. All objects dropped from the same height on the Moon will hit the ground at the same time.

12. Kepler improved on Copernicus' heliocentric model by using ellipses to describe the orbits of the planets.

13. The primary reason for using telescopes with larger primary mirrors for astronomical observations is to collect more light to see fainter objects.

14. If there are two identical stars, but one is twice as far away from the observer as the other one, the more distant one will appear to be four times fainter than the closer one.

15. There no X-ray telescopes on the surface of the Earth because X-ray photons are not able to pass through the atmosphere.

16. If you have two glowing bodies, you can tell which one is hotter because the hotter one has a bluer color (this generally works for stars).

17. Photons all travel through space at the same speed.

18. Radioactive atoms with experimentally determined half-lives can be used to age date rocks.

19. Measuring the periods and radii of the orbits of the moons around giant planets like Jupiter allows us to determine the mass of Jupiter through Kepler's and Newton's Laws.

19. The measured age of the solar system and of the Earth is approximately 4.5 billion years (4,500,000,000 years).

20. The correct chronological order is Copernicus-Kepler-Newton.

21. Being on a planet the same size as Earth but with twice the mass would double your weight.

22. The giant planets and the Sun are composed mainly of hydrogen and helium.

23. The mass of the Sun is more than 99\% of the total mass of the Solar System.

24. The development of the Ozone layer was important for the development of life forms on land because ozone blocks harmful UV radiation from the Sun.

25. Venus has such a thick atmosphere compared to Earth because it is closer to the Sun, so it was hotter, which led to evaporation of some its water, which freed up carbon dioxide, which made the surface hotter, which evaporated more water, releasing more carbon dioxide to make a thick atmosphere.

26. The surface of Venus is hotter than its upper atmopshere because the greenhouse effect warms the surface.

27. If a solar system was forming around a star that was hotter than the Sun, the most likely place to find a habitable planet with an Earth-like atmosphere would be farther away from the star than the Earth is from the Sun.

28. The giant planets are all composed primarily of Hydrogen.

28. Lunar craters were caused by meteoric impacts.

30. CO2 (Carbon dioxide) is most responsible for the greenhouse effect in the inner solar system.

31. Of the large inner moons of Jupiter, Io is the closest to the planet itself. Io is also very active, with significant volcanism. The source of energy for Io's activity is tidal heating from gravitational interaction with Jupiter.

32. Uranus probably collided with another large object because it rotates about an axis that is perpindcular to its orbit.

33. What is actually measured in the Doppler technique that indicates the presence of a massive planet? The systematic shifting to shorter and longer wavelengths of light observed from the star.

34. The material in Saturn's inner rings can not clump together into moons because they are very close to Saturn, so the gravitational tidal forces tear them apart and do not allow then to clump together.

35. The Earth has a modest ``natural'' greenhouse effect that warms the planet by about 20 degrees Centigrade.

36. There so many craters on the Moon and not on the Earth because the Earth is still geologically active and the Moon has not been active for a long time.

37. Pluto has the most elliptical (least circular) orbit of all of the planets.

38. The great distance to even the most nearby star makes it highly unlikely we will be able to travel to any other solar system

39. Only massive planets been discovered so far with the Doppler technique because more massive planets exert a stronger gravitational force on their star, and available technology can only detect fairly sizeable velocity changes.

40. The Earth has less Hydrogen than the Sun and the giant planets because when the planets were forming, the inner solar system was too hot for light elements and compounds to condense onto protoplanets.

41. A protostar collapses when its gets dense enough so gravity pulls it together.

42. The Sun gets its energy from the fusion of Hydrogen into Helium.

43. Most of the Sun's energy is produced in the inner core.

44. Convection is one of the ways many stars transfer energy from their centers to the outer regions. Convection is the movement of hot material into colder regions.

45. Most stars, when plotted on the usual Hertzsprung-Russell diagram (luminosity vs. temperature), fall into a region astronomers call the main sequence.

46. The characteristic of a star that determines where it will be on the main sequence is its mass.

47. Why are the less massive stars (like the Sun) NOT able to produce elements heavier than carbon and oxygen? Because the star's center cannot get hot and dense enough for the nuclear reactions that build heavier nuclei.

48. The most massive stars have the shortest lives.

49. If you see a cluster of stars without any bright, blue stars, you can infer that it is a old star cluster.

50. Red giant and supergiant stars are cool and have large diameters.

51. Stars evolve from the main sequence to become giants when they have turned their cores from hydrogen into helium.

52. Ultimately, fusion produces energy because E=mc^2 and the heavy element that results from fusion is a little bit less massive than the lighter elements that were combined to make it.

53. Massive stars evolve so they have iron cores and may explode as supernovae.

54. Harlow Shapley figured out that the Sun was not at the center of our Milky Way Galaxy because most of the globular clusters are on one side of the sky, which should not happen if the Sun was in the center of the Galaxy.

55. The iron and other heavy elements in the universe were produced by nuclear reactions that occur inside massive stars.

56. Our Milky Way galaxy is a spiral galaxy.

57. The primary line of reasoning leading to the discovery of large amounts of dark matter around galaxies is that observations of the Doppler shift in the outer regions of galaxies show rapid motions of stars and gas, indicating that there is a lot of mass, but we do not see any corresponding light.

57. What is the evidence that elliptical galaxies are not forming stars and have not done so in some time? They do not have bright, blue stars.

58. We know "nebulae" are galaxies of their own well outside of our Milky Way Galaxy because we have observed Cepheid variable stars and determined distances that place them well beyond our own Galaxy.

59. The orbits of stars in an elliptical galaxy are in almost completely random directions, often with orbits that are not perfectly circular.

60. If you see a galaxy that has some ongoing star formation and is flattened like a frisbee or a plate, it is a spiral galaxy.

61. There are billions of stars in our Milky Way galaxy.

62. The component of our Milky Way Galaxy that contains the most mass is the dark matter.

63. The source of the very high luminosities (intrinsic brightness) of quasars and QSOs is radiation from material falling onto a black hole.

64. The evidence that there is a massive black hole at the center of our Galaxy is that the orbits of stars very close to the Galactic center indicate that there is a very massive, dense object at the center.