Across
- 2. the distance from the Earth to the Sun
- 8. patterns seen in groups of stars in the sky
- 9. the unit of distance most used by astronomers
- 11. an object that orbits a star but has not cleared the path of other objects
- 14. Greek who calculated the radius of the Earth
- 17. a.k.a. longitude
Down
- 1. the distance light travels in one year
- 3. invented to try to explain retrograde motion
- 4. the study of objects beyond Earth and how they interact
- 5. a collection of dust, gas, stars & planets
- 6. the point in the sky directly overhead
- 7. a science rule that has never been disproven
- 10. oval shape of planetary orbit
- 12. the direction pointed in the sky measured in degrees
- 13. belief that the Earth is the center of everything
- 15. how high an object is above the horizon
- 16. the movement of one object around another
- 18. giant balls of hot plasma that give off radiation