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