1. Earth
Basics
Something
To Model
Planets
And the
Night Sky
Johannes
Kepler
Isaac
Newton
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2. This is the third planet from the sun.

3. What is the Earth?

4. Although Earth’s orbit appears to be circular, it is actually what.

5. What is an Ellipse?

6. This is the force of attraction that exists between all matter.

7. What is gravity?

8. The average distance between the Earth and the Sun is known as a(n)?

9. What is an Astronomic Unit (AU)?

10. “The attraction between two objects depends on the masses of the objects and the distance between the objects” is a re-statement of this scientific law.

11. What is Newton’s Law of gravitation?

12. Who explained retrograde motion by having planets move in small circles around their orbital path around Earth?

13. Who was Ptolemy?

14. The simplest and most straightforward explanation of observations is most likely to be correct is know as what?

15. What is Occam’s razor?

16. Who discovered that Venus exhibited phases like those of the Moon?

17. Who was Galileo Galilei?

18. The true orbital period of a planet (one full orbit of the planet relative to the background stars) is know as what?

19. What is a Sidereal Period?

20. Who do we generally credit for coming up with a working heliocentric model?

21. Who was Nicolaus Copernicus?

22. The word planet came from a Greek word with what meaning?

23. What is Wanderer?

24. The occasional westward movement of a planet with respect to the background stars is called what?

25. What is Retrograde Motion?

26. Who first saw the rings around Saturn?

27. Who was Galileo Galilei?

28. An inferior planet at greatest eastern elongation is known as a “Morning Star” or “Evening Star”?

29. What is an “Evening Star”?

30. An inferior planet at greatest western elongation rises in the east before or after the Sun?

31. What is Before the Sun?

32. Kepler’s first law states that the orbit of a planet is an ellipse with what at one of the foci?

33. What is the Sun?

34. The semi-major axis of a planet’s orbit is the average distance between what?

35. What is the Planet and the Sun?

36. Kepler’s second law states that a line joining a planet and the Sun sweeps out equal areas in equal intervals of what?

37. What is Time?

38. Kepler’s third law says that the larger a planet’s orbit the longer it takes for what?

39. What is Complete one Sidereal Period (Orbit)?

40. While Kepler’s laws were a landmark in history, he was still unable to explain what about the planetary movement that followed his laws?

41. What is “Why” the Planets moved as the did?

42. According to Newton’s first law, if no net outside force acts on a moving object, it can only move in a straight line and at a what?

43. What is a constant speed?

44. If a planet is slowing down or changing direction it is doing what according to Newton’s second law of motion?

45. What is Accelerating?

46. If you try to jump out of a boat and the boat moves backwards, this is an example of which of Newton’s laws?

47. What is Newton’s Third Law of Motion?

48. In Newton’s law of universal gravitation what two properties determine the gravitational force.

49. What are Mass and Distance?

50. What two forces keep a planet in orbit?

51. What is Gravity and Forward Momentum?