Sheldon Cooper Knows What?

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Across
  1. 3. Infinitely dense and Infinite Gravity
  2. 6. Sun blocked by Earth, Moon is Red
  3. 8. Gas Cloud
  4. 10. Very dense and hot and small star
  5. 12. Collection of Galaxies
  6. 16. measures brightness and temperature to determine size/category of star
  7. 18. Big ball of hot gas
  8. 19. Large Explosion of a Star
  9. 20. the force of attraction between all masses in the universe
Down
  1. 1. Sun blocked by Moon.
  2. 2. Theory that the universe was in one small space and exploded
  3. 4. Remnant of Red Giant
  4. 5. Star Explosion
  5. 7. Rapid spinning neutron star emitting radio pulses
  6. 9. Very Large Explosion of a star
  7. 11. a small celestial body composed of rock and metal
  8. 13. Active Galactic Nucleus of High Luminosity
  9. 14. Everything with Empty Space
  10. 15. 9.5 Trillion kilometers in 1 year.
  11. 17. Collection of stars