| A | B |
|---|
| galaxy | A giant structure that contains hundreds of billions of stars. |
| universe | All of space and everything in it. |
| light-year | The distance that light travels in one year. |
| parallax | The apparent change in position of an object when seen from different places. |
| giant star | A very large star, much larger than the sun. |
| apparent magnitude | The brightness of a star as seen from Earth. |
| absolute magnitude | The brightness of a star if it were a standard distance from Earth. |
| Hertzsprung-Russell diagram | A graph relating the temperature and brightness of stars. |
| main sequence | An area on the Hertzsprung-Russell diagram that runs from the upper left to the lower right and includes more than 90 percent of all stars. |
