Universe

3. Fusion A nuclear reaction combining small atoms into larger atoms
5. Microwave Background Radiation Electromagnetic waves from the Big Bang that have expanded to microwave frequency in the background of the universe
8. Force Attractive force between protons and neutrons in an atom's nucleus
9. Everything physical - matter and energy - that exists in space and time
10. Fission A nuclear reaction splitting large atoms into smaller atoms
11. A cloud of dust and gas in space likely to produce stars or planets
13. Star The end stages of a smaller star's life including losing outer layers then the hot inner core cooling
15. The result of a supergiant star imploding and blasting away its outer layers
17. Hole One possible end to a giant star's life, caused by its core collapsing and vanishing
18. The energy or brightness of a star
20. Decay A nuclear reaction involving the spontaneous decay of unstable atoms
21. Radiation Extra high energy radiation released when a radioactive atom changes into a new stable atom
24. Term for an atom with an unstable nucleus that is emitting large amounts of radiation (energy)

1. The amount of time in takes for half of a radioactive sample to decay and become stable
2. Diagram A graph plotting stars by temperature and luminosity
4. Radiation Result of a radioactive atom converting one neutron into a proton and an electron to become a new stable atom
6. Effect/Shift An observed change in frequency when the source of a wave or the observer is moving
7. A large group of gas, dust, stars and satellites held together by gravity
12. Law The further away a galaxy is, the faster it is moving away
14. Force A force that allows elementary particles to transform
16. Radiation Result of a radioactive atom losing 2 protons and 2 neutrons to become a new stable atom
19. Star One possible end to a giant star's life, caused by its core collapsing to a very dense state
21. Star The second stage in a star's life cycle - red giant or super giant.
22. Sequence Star A young star in the early, stable stage of its life cycle
23. Bang Theory Theory of the origin and evolution of the universe