Earth, Moon, and Sun.

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Across
  1. 2. the border between light and dark on the Moon
  2. 6. the amount of time it takes for a planet to complete one orbit around a star or stars
  3. 9. a moon phase in which the Moon is not visible from Earth
  4. 10. the relative size of things
  5. 11. an object, diagram, or computer program that helps us understand something by making it simpler or easier to see
  6. 13. a moon phase that looks like a full circle from Earth
  7. 14. a moon outside our solar system
  8. 15. the star that is the main source of light at the center of our solar system
  9. 16. the nearly circular path a smaller object (like the Moon) travels around a larger object (like Earth).
  10. 18. moon phase that looks like less than half a circle from Earth
  11. 19. the shape of the illuminated part of the Moon as it appears from Earth
Down
  1. 1. a moon phase that looks like more than half a circle from Earth
  2. 3. a planet outside our solar system
  3. 4. something we observe to be similar over and over again
  4. 5. the sun, the planets that orbit the sun, and other objects that orbit the sun
  5. 7. a rocky sphere that travels around a planet
  6. 8. shine light on an object and make it visible
  7. 12. the Moon is completely dark
  8. 17. a moon phase that looks like a half-circle from Earth