Across

1. When the gravitational forces on an object in space are balanced
7. An object in space that orbits a star
8. The ninth planet from the Sun
9. The seventh planet from the Sun
12. When two forces on an object are equal in size but opposite in direction
13. The SI unit of force
16. The closest planet to the Sun
17. The force acting on an object due to its mass
19. The fifth planet from the Sun
20. An object in space that emits light
21. An object in space that orbits a planet

Down

2. The third planet from the Sun
3. The sixth planet from the Sun
4. The Earth's natural satellite
5. The fourth planet from the Sun
6. The eighth planet from the Sun
10. Everything that exists anywhere
11. A collection of many stars
14. When a satellite blocks light from a star
15. The path that an object travels on through space
18. The second planet from the Sun