1. The period of rotation of the Earth.
3. The point in a planet's orbit where it is closest to the sun.
5. A book of planetary positions.
7. The tendancy for things to keep doing whatever they are doing.
14. Kepler found that planets follow orbits that are of this shape.
15. When a planet appears closest to the Sun in our sky.
17. The plural form of "focus".
19. The period of revolution of the Earth.
2. The point in a planet's orbit where it is farthest from the sun.
6. Movement around an other object.
9. The apparent path of the Sun, Moon, and planets in out sky.
10. The _____ of an ellipse is the distance between the foci divided by the length of the major axis. A measure of how "out of round" the ellipse is.
11. When a planet appears 180 degrees away from the Sun in our sky.
12. Backward (westward) motion of a planet.
13. Abbreviation for the distance from the Earth to the Sun.
16. The singular form of "foci".