Houston, We Have a (Word) Problem...

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Across
  1. 4. A property of light and motion, makes things 'redder'
  2. 6. They don't just make rockets, ya know
  3. 7. Niels didn't want to be a ____
  4. 8. __U a favor
  5. 12. Good for stars, bad for balloons
  6. 13. A collection of stars that appear close
  7. 15. Jean pants or ____ Krantz?
  8. 16. My essay about The Moon's gravity could sure use a _____
  9. 17. The particle accelerator is cause for con____
  10. 19. A teaspoon of me weighs as much as a mountain
  11. 21. The machine will help, the pressure will hurt
  12. 23. We're on the same __________
Down
  1. 1. Mickey and his dog _____
  2. 2. Quark is a _______ fella
  3. 3. The ____ side of The Moon, often confused with the far side
  4. 4. Can cure cancer or cause it
  5. 5. Not because they are easy, but because they are hard
  6. 9. If you're a dwarf and you're _____, you're real dense
  7. 10. See you ____
  8. 11. An infinitely dense point in space
  9. 14. Make it big in acting and you'll be a ____
  10. 18. Hulk Smash!
  11. 20. 5...4...3...2...1...
  12. 22. One day the Sun will be a ___ giant.