Star colors reveal surface temperature, with bluish stars hotter than reddish ones.

The longer version

Stellar color tracks temperature because a star radiates roughly like a blackbody, with the peak wavelength shifting toward the blue as the surface grows hotter. Cool stars peak in the red and infrared, while hot ones put out more blue and ultraviolet light. The Sun sits near the middle of that range and appears yellowish.

Astronomers classify stars by spectral type using absorption lines as well as color, which reveals composition alongside temperature. Apparent brightness depends on distance too, so color is a far more reliable guide to a star's physical state than how bright it looks. Red stars can be either small and dim or huge and luminous.

Where this entry sits

The night sky looks calm, yet almost everything up there is moving, burning, or slowly changing. These facts cover planets, stars, the Moon, gravity, black holes, comets, and the story of how people began exploring beyond Earth. The full list sits on the Space and Sky page, where every entry is listed in order.