| A | B |
|---|
| hottest stars | blue color |
| coolest stars | red color |
| astronomers study | light from stars |
| spectrum | millions of colors |
| spectroscope | instrument to separate light |
| hot gases | give off wavelengths of light |
| every element | unique set of emission lines |
| absorption spectrum | light passes through less dense, cooler gas |
| hydrogen and helium | what stars are mostly made up of |
| how stars are classified | how hot a star is |
| apparent magnitude | brightness of a star |
| absolute magnitude | brightness of star if it was 32.6 light years away |
| light-year | how far light travels in a year |
| daytime and nighttime | caused by the Earth rotating |
| seasons | caused by the tilt of the Earth and revolution |
