Space

2. An empty space that doesn't have any matter.
4. A set that includes a star and all of the matter that orbits it, including planets, moons, asteroids, comets, and other objects.
6. An icy rock that lets off gas and dust, which may form tails when it is flying close to a sun.
7. A vehicle used for traveling in space.
8. Rocks floating around in space. Some are the size of a pick-up truck. Others are hundreds of miles across.
10. A large body in outer space that circles around the sun or another star.
12. All of space and time, and everything in it.
14. A natural object that travels around a bigger natural object.
15. The energy or particles released from sources like radioactive materials, explosions, and chemical reactions.
16. The star in the center of our solar system.
17. The curved path that a planet, satellite, or spacecraft moves as it circles around another object.

1. How we describe some atoms that are unstable. They change into different kinds of atoms and release lots of energy.
3. An object that orbits another object
4. a ball of shining gas, made mostly of hydrogen and helium, held together by its own gravity.
5. The amount of matter something is made of.
9. The explosion of a star that makes it as bright as a whole galaxy.
11. The gases held by gravity around Earth and around other planets
13. A force that pulls matter together.