Betelgeuse

Betelgeuse (Alpha (α) Orionis) is a semiregular variable star located 427 light-years away. It is the second brightest star in the constellation Orion, and the ninth brightest star in the night sky. Although it has the Bayer designation "alpha", it is not as bright as Rigel (Beta Orionis). It is a vertex of the Winter Triangle asterism.

Betelgeuse is a red supergiant, one of the largest stars known. If it were placed at the center of our solar system, its outer surface would extend between the orbit of Mars and Jupiter. The angular diameter of Betelgeuse was first measured in 1920–1921 by Michelson and Pease using an astronomical interferometer on the Mount Wilson 100 inch telescope.