Cosmic Conundrums: A Space-Themed Crossword Challenge

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Across
  1. 4. The natural satellite of Mars
  2. 9. The phenomenon where a planet's orbit causes it to pass in front of a star
  3. 10. The effect that causes light from galaxies to shift to the red end of the spectrum
  4. 11. The most abundant gas in the universe
  5. 14. The expansion of the universe was discovered by this astronomer
  6. 16. The galaxy closest to the Milky Way
  7. 17. Largest dwarf planet in the asteroid belt
  8. 19. The theoretical boundary marking the limit of a black hole
  9. 20. The outermost layer of a star's atmosphere
  10. 21. The second-largest moon of Neptune
Down
  1. 1. The spacecraft that took humans to the Moon
  2. 2. Bright streak in the sky from a meteoroid entering Earth's atmosphere
  3. 3. This particle is responsible for light and electromagnetic radiation
  4. 5. The point where light can't escape a black hole
  5. 6. The largest moon of Saturn
  6. 7. The force that resists changes in motion
  7. 8. Distance light travels in one year
  8. 12. The speed necessary to break free from a planet's gravitational pull
  9. 13. The smallest planet in the solar system
  10. 15. The type of star our Sun is classified as
  11. 18. The name of Earth's closest star