Earth, Sun, Moon.

3. To follow a path.
5. The envelope of gases surrounding the Earth or another planet.
7. The laying down of sediment carried by wind flowing water, the sea, or ice.
8. A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
12. The stellar object that the Earth revolves around.
13. An imaginary line about which the Earth rotates.
16. A burning ball of gas.
18. A system of stars, planets, moons, and other objects, bound together by gravitational orbit.
19. The planet we live on.
20. The process of eroding or being eroded by wind, water or other natural agents.
21. The lowest region of the atmosphere, extending from the Earth's surface to a height of about 3.7-6.2 miles (6-10 km), which is the lower boundary of the stratosphere.
23. The Earth's only natural satellite.
24. A celestial body orbiting the Earth or another planet.
25. When the Moon blocks out the sun.

1. An imaginary line drawn around the Earth equally distant from both poles, dividing the Earth into northern and southern hemispheres and constituting the parallel of latitude 0°.
2. To spin.
4. The force that attracts a body toward the center of the earth, or toward another physical body having mass.
6. To orbit.
9. An astronomical event where the Moon moves into the Earth's shadow, causing it to darken.
10. Holes made for an asteroid or meteor.
11. The region of the Earth's atmosphere above the mesosphere and below the height at which that atmosphere ceases to have the properties of a continuous medium.
14. The region of the Earth's atmosphere above the stratosphere and below the thermosphere.
15. The part of the Earth's atmosphere which extends from the top of the troposphere to about 30 miles (50 kilometers.)
17. The process of eating or being worn down by long exposure to the atmosphere.
22. There are eight of these in our Solar System.