Across
- 2. The more ___ an object has, the stronger its gravitational pull
- 6. Common word derived from the Greek word "wanderer"
- 7. Physicist who proposed that gravity is really just the warping of spacetime
- 9. Type of model that had Sun, Moon & planets orbiting Earth
- 10. The apparent "backward" (westward) motion of planets
- 11. Actual shape of planetary orbits, like a flattened circle
- 13. Scientist who discovered the law of universal gravitation, and other basic laws of motion
- 14. An imaginary line connecting the Sun to a planet sweeps out equal ___ in equal time intervals
- 15. The average distance from Earth to Sun is one ___ unit
- 16. Astronomer who developed three laws of planetary motion
- 19. A small circular orbit that moves around a larger orbit
- 21. Astronomer who proposed Earth-centered model with 55 crystalline spheres
- 22. Measure of how flattened an orbit is; "0" is perfect circle, "1" is straight line
Down
- 1. The force that attracts planets to the Sun
- 3. An ancient observatory in England built during the Stone Age
- 4. Astronomer who first used a telescope to discover four moons around Jupiter
- 5. Astronomer who revived heliocentric model in the 1500s
- 6. Astronomer who used epicycles to explain planetary motion
- 8. First astronomer to create a heliocentric model
- 11. Speed needed to overcome Earth's gravity and move away from Earth
- 12. Force of gravity obeys a(n) ___-___ law: it decreases rapidly with distance from source
- 17. Type of model that had all planets orbiting Sun
- 18. Astronomer who took incredibly detailed data of the sky from his home observatory
- 20. Time for planet to complete one orbit