Hertzsprung-Russell+Diagram

This graph was created in the early 1900s (about one hundred years ago) and is still used today! It's very good in graphing brightness, color, temperature, and size.

For example, if we take the star Alkaid on a recent Hertzsprung-Russell Diagram we can tell it is in its main sequence (so it is average sized), it has the luminosity it is about 300 times the luminosity of the Sun, and its surface temperature is about 20,000 Kelvins.