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ACROSS 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". 18. Spinning. 19. The period of revolution of the Earth.  | 
    
DOWN 2. The point in a planet's orbit where it is farthest from the sun. 4. Sun-centered. 6. Movement around an other object. 8. Earth-centered. 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".  |