Our universe

1. Planets whose orbit is within the asteroid belt, including Mercury, Venus, Earth and Mars.
6. A push or pull on an object when it interacts with another.
10. A regular and repeating circuit that one celestial object takes around another.
11. A system of two stars where one revolves around the other or both revolve around a common centre.
13. The area of air and gas that envelopes Earth and other astronomical objects.
15. The region between Mars and Jupiter that contains the largest population of asteroids in our solar system.
17. The main theory explaining how the universe started. It states that 13.8 billion years ago, space expanded quickly to form the atoms that would produce stars and galaxies.
20. A person trained to travel in a spacecraft.
22. A body in space that resembles a small planet but lacks criteria to class it as such.
23. Small, rocky objects that orbit the Sun.

2. When one celestial body blocks light from reaching another by moving between it and its light source.
3. Small dim galaxies that are abundant in the universe.
4. Planets whose orbits are outside the asteroid belt, including Jupiter, Saturn, Uranus and Neptune.
5. A large celestial object that acts as a natural satellite to Earth. Most planets in our solar system have at least one moon and some have several.
7. A celestial body that orbits the sun that has sufficient mass for its gravity to overcome rigid body forces and has not cleared the neighbourhood around its orbit.
8. The force that pulls objects towards each other.
9. A building equipped with materials to make astronomical observations.
12. A scientist who studies the universe.
14. One object revolving around another in an oval shape. The shape is known as an ellipse.
16. A cloud of dust and gas in space.
18. Basic units of matter that every solid, liquid gas and plasma is composed of.
19. A small star with low luminosity.
21. A huge collection of gas, dust and billions of stars and their solar systems held together by gravity.