Earth, Moon, Sun

2. the shape of the illuminated part of the Moon as it appears from Earth
4. a moon outside our solar system
5. a moon phase that looks like less than half a circle from Earth
7. when the Moon is completely dark
12. to shine light on an object and make it visible
13. the amount of time it takes for a planet to complete one orbit around a star or stars
14. an object, diagram, or computer program that helps us understand something by making it simpler or easier to see
15. the sun, the planets that orbit the sun, and other objects that orbit the sun
18. a moon phase in which the Moon is not visible from Earth

1. the border between light and dark on the Moon
3. a rocky sphere that travels around a planet
4. a planet outside our solar system
6. a moon phase that looks like a half-circle from Earth
8. a moon phase that looks like a full circle from Earth
9. a moon phase that looks like more than half a circle from Earth
10. something we observe to be similar over and over again
11. the nearly circular path a smaller object (like the moon) travels around a larger object (like Earth)
16. the relative size of things
17. the star that is the main source of light at the center of our solar system