Red Giant
Image from Steve Bowers

An old, post-main-sequence, star, usually spectroscopic class K or M but also including class S and most carbon stars. Red giants have relatively low temperatures and surface layers which have have expanded to many solar radii. However, because they are so large, they are also very luminous.

A typical Sol-like star will eventually expand into a red giant; in fact a star of one solar mass will enter two separate red giant phases, the second one known as the Asymptotic Giant Branch due to its location and shape on the Hertzsprung-Russell diagram.
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Development Notes
Text by M. Alan Kazlev
Initially published on 22 December 2001.