Betelgeuse is a red supergiant star in the constellation Orion. It marks the hunter’s shoulder in the familiar hourglass-shaped figure and is usually Orion’s second-brightest star after the blue supergiant Rigel.
Its orange-red color comes from its relatively cool surface compared with hot blue stars, although Betelgeuse is vastly larger and more luminous than the Sun. It is a semiregular variable star, changing in apparent brightness over cycles of roughly 400 days. Because it is near the end of its short, massive-star life, astronomers expect it eventually to explode as a supernova, though not on a predictable human timetable.
Betelgeuse is also called Alpha Orionis, the Bayer designation assigned to it in 1603. Its name ultimately derives from an Arabic expression associated with Orion’s hand, complicated by medieval copying and transliteration errors. It is often confused with Rigel because both are prominent supergiants in Orion, but Rigel is blue-white while Betelgeuse is distinctly red.