y

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Across
  1. 2. a huge group of stars, gas, and dust
  2. 4. a planet outside our solar system
  3. 5. energy that travels through space
  4. 9. the movement of one object around another
  5. 13. the layer of gases around a planet
  6. 15. a scientist who studies space
  7. 16. a type of light from the sun we cannot see
  8. 17. the thick layer beneath a planet’s crust
  9. 18. half of a planet
Down
  1. 1. the vast space that contains all stars and galaxies
  2. 2. the force that pulls objects toward each other
  3. 3. an imaginary line an object spins around
  4. 6. a cloud of gas and dust in space
  5. 7. the center part of a planet
  6. 8. a type of light we cannot see that gives heat
  7. 9. the spinning of an object on its axis
  8. 10. the outer layer of a planet
  9. 11. an object that moves around a planet
  10. 12. a space rock that lands on Earth
  11. 14. the amount of matter in an object