Module 7: Stars

The light from every star, except the Sun, has traveled for many years just to shine in the sky each night. Some of the stars still seen have long since burned out, but the light still travels to Earth. It is amazing that these objects, which are so far away, can still be studied. Before you began this module, you may not have known that stars have a life cycle. They begin in a nebula, and then travel through a very long life cycle, until they end up in a death that could include a black hole, or white dwarf.

Not all stars are created equal. Some stars will travel down the main sequence, while others will not be able to control their fusion and will get large very quickly. Some stars will fade away, becoming dwarfs, while others will explode in the most spectacular of all fashions as supernovas.

All stars are classified and represented on the Hertzsprung-Russell (H-R) diagram. On this diagram, stars are organized by their luminosity and their temperature. As seen on the H-R diagram, the Sun is a middle-aged, medium luminous star. Star color is associated with temperature. The hottest stars are blue and the coolest stars are red.