Science cross word puzzel

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Across
  1. 3. is a type of satilight
  2. 6. NASA
  3. 7. force/acceleration
  4. 8. substance that is the simplest member of the family of chemical elements
  5. 11. were we live
  6. 13. a giant cloud of dust and gas in space
  7. 14. A snow machine brand
  8. 16. a property of matter by which it remains at the state of rest or in uniform motion in the same straight line unless acted upon by some external force
  9. 17. a place in space where gravity pulls so much that even light can not get out
  10. 18. what is keeping us in orbit..
  11. 21. the distance light travels in one year
Down
  1. 1. A hour and a half is equal to___
  2. 2. a group of stars that forms a particular shape in the sky and has been given a name.
  3. 4. a doughnut-shaped ring of icy objects
  4. 5. an Ethiopian princess of Greek mythology rescued from a monster by her future husband Perseus
  5. 8. Telescope
  6. 9. a moon, planet or machine that orbits a planet or star
  7. 10. a broad band of light that can be seen in the night sky and that is caused by the light of a very large number of faint stars
  8. 12. a star system, and is widely believed to be the closest to the solar system at a distance of 4.37 light-years
  9. 15. a regular, repeating path that one object in space takes around another one
  10. 18. a huge collection of gas, dust, and billions of stars and their solar systems
  11. 19. a celestial body that revolves around a star
  12. 20. "twinkle twinkle little star______"