Across
- 5. number of other known earth sized planets with large moon
- 9. physical state of earth's iron core
- 12. planet that crashed into early earth
- 13. type of field surrounding and protecting earth
- 14. built giant towers to observe planets
- 15. necessary to confirm a hypothesis
- 16. June 21
- 17. brought water to earth during unstable epoch
- 18. caused the early odd shaped earth to become a sphere
Down
- 1. stabilizes incline of earth promoting reliable seasons
- 2. dangerous period for earth "war of the titans"
- 3. form of the earth 4.5 billion years ago,prior to becoming rocky
- 4. season when northern hemisphere is tilted toward the sun
- 6. midpoint between summer and winter solstice
- 7. proposed sun centered solar system
- 8. initial force to bind pre-earth dust particles
- 10. discovered moons orbiting Jupiter
- 11. Kepler's proposed shape of planet orbits