| A | B |
|---|
| Nuclear fusion | The process by which two or more small nuclei fuse to make a bigger nucleus |
| Nuclear fission | The process by which a large nucleus is split into smaller nuclei |
| Critical mass | The amount of isotope necessary to sustain a chain reaction |
| Absolute magnitude | The brightness of a star, corrected for distance, aon a scale of -8 to +19. The smaller the number, the brighter the star. |
| Apparent magnitude | The brightness of a star as seen in the night sky. The smaller the number, the brighter the star. |
| Light year | The distance light could travel along a straight line in one year |
| Galaxy | A large ensemble of stars, all interacting through the gravitational force and orbiting around a common center |
