Across
- 2. telescope with a lens that bends light
- 4. added an extra day every fourth year to calendar
- 5. attractive force between two objects
- 6. telescope that uses a curved mirror
- 8. most popular theory for formation of moon
- 11. planet with a deep atmosphere; not very dense
- 12. a layer of crushed rock on the lunar surface
- 13. dark, large areas of lunar basalt
- 15. the process in which fluids move due to temp
- 17. movement of a body around another
- 18. developed the heliocentric theory
Down
- 1. tendency for a body to remain in motion
- 3. point at which Earth is closest to the sun
- 7. spin of a body on its axis
- 9. system created for measuring long time periods
- 10. bowl-shaped depressions on the moon
- 14. study of the universe
- 16. an instrument that allows one to see distantly