# Star colour

Also called: star color, colour index, B−V.

Stars are coloured by their temperature: blue-white stars are the hottest, orange and red the coolest.

A star glows like a hot coal. The hottest stars, above 10,000 °C, shine blue-white (Rigel, Vega); the Sun, at about 5,500 °C, is yellow-white; cooler stars are orange (Arcturus) or red (Antares, Betelgeuse). Astronomers label them O, B, A, F, G, K and M from hottest to coolest.

Colours are subtle to the eye but easiest to see in contrasting [doubles](https://astropilot.space/glossary/double-star) — Albireo's gold and blue — and in slightly defocused bright stars.

**Examples:** [albireo](https://astropilot.space/object/albireo.md), [antares](https://astropilot.space/object/antares.md), [rigel](https://astropilot.space/object/rigel.md), [iota-cancri](https://astropilot.space/object/iota-cancri.md)

**Related:** [Double star](https://astropilot.space/glossary/double-star.md), [Magnitude](https://astropilot.space/glossary/magnitude.md), [Spectral type](https://astropilot.space/glossary/spectral-type.md)

From the AstroPilot astronomy glossary: https://astropilot.space/glossary/star-colour