| A | B |
|---|
| star systems | groups of two or more stars |
| eclipsing binary stars | become dimmer at regular intervals |
| elliptical | type of galaxies with almost no gas or dust |
| a very slight back and forth motion | one indication that a planet may exist near a star |
| spiral | the Milky Way is this type of galaxy |
| Milky Way | the galaxy our sun is part of |
| big bang | theory developed to describe the formation of the universe |
| 10 to 15 billion years old | approximate age scienctists think our universe |
