Outer space

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Across
  1. 3. the fourth state of matter
  2. 4. a powerful and luminous explosion of a star
  3. 5. a group of visible stars, which forms a perceived pattern
  4. 8. the reason why there's no sound in space
  5. 11. a famous space telescope
  6. 12. known as the "red planet"
  7. 14. a unit for measuring temperature in space
  8. 15. a tunnel between two distant points in our universe
  9. 16. the study of outer space
  10. 17. the most common element in the universe
  11. 18. the only known habitable planet
  12. 19. the sun is a...
Down
  1. 1. an alien spaceship is also called a...
  2. 2. a single four-dimensional continuum
  3. 6. a layer of gas that envelop a planet
  4. 7. a star-forming region
  5. 9. the nearest galaxy to ours
  6. 10. a region of space where gravity is so strong that nothing can escape it (2 wds.)
  7. 12. Earth's only natural satellite
  8. 13. what a shooting star actually is