Space

3. The density of energy emitted by or absorbed from a light source
5. A luminous object consisting mostly of hydrogen and helium, held together by its own gravity.
10. The distance from one object in space to another object.
13. To give out
14. Half a sphere
15. Bounce back (heat, light, or sound) without absorbing it.
16. The curved path of an object or spacecraft round a star, planet, or moon.
18. The angle between the direction of the poles and the normal (at a right angle) to the plane of orbit.
19. The collection of eight planets, their moons, dwarf planets and other natural satellites that orbit around the Sun.
21. A natural object that orbits a planet or asteroid.
22. The distance that light travels in one year.
23. An orbit with an orbital period that matches the Earth's rotation. It takes 24 hours to complete one revolution.

1. Made or produced by human beings rather than occurring naturally.
2. The star at the centre of our solar system.
4. An object that orbits a star, has sufficient mass to be round or nearly round, and has removed the debris and small objects from the area around its orbit.
5. The changes in weather, and hours of daylight caused by the tilt of the Earth as it orbits the Sun.
6. All existing matter and space
7. The total or partial obscuring of one celestial body by another.
8. A particular appearance or state in a regularly recurring cycle of changes.
9. An object that moves around another object.
11. Existing in or derived from nature, not man made or caused by humankind.
12. The movement of one object around another object
13. The third planet from the Sun
17. A collection of stars and their solar systems, gas and dust, all held together by gravity.
20. Spinning about a central axis