Hertzsprung–Russell diagram
As you can see, stars tend to fall only into certain regions of the diagram when graphed in this way. All stars in a given area of a Hertzsprung-Russell diagram share similar luminosities and temperatures. The main region where stars appear is the diagonal curved line, going from the upper-left (hot and bright) to the lower-right (cooler and less bright). This is called the Main Sequence. Above the main sequence is another region containing the red giants and supergiants. Below is a curved line representing the white dwarfs.