Giant and Super Giant stars

At the upper right of the H-R diagram, above the main sequence, stars are brighter than main-sequence stars of the same color. The only way stars of a certain color can be brighter than other stars of the same color is if the brighter stars are also bigger. Bigger stars are not necessarily more massive, but they do have larger diameters. Stars that fall in the upper right of the H-R diagram are known as giant stars or, for even brighter stars, supergiant stars. Supergiant stars have both larger diameters and larger masses than giant stars.

Giant and supergiant stars represent stages in the lives of stars after they have burned most of their internal hydrogen fuel. Stars swell as they move off the main sequence, becoming giants and—for more massive stars—supergiants.