Questions about α Orionis, the red supergiant star located in the "shoulder" of the constellation Orion.
Betelgeuse is a variable star in the red supergiant branch of stellar evolution. Although it is designated by the letter α, it is often not the brightest star in the Orion constellation and is outshined by Rigel.
Betelgeuse is a semi-regular variable star with a period of 5.7 years. Over this time, its apparent magnitude can vary between 1.3 and 0. Starting in late 2019, its magnitude has further dropped to 1.5.
It is a red supergiant -- a very large cool star towards the end of its lifespan -- with a radius of 4.3 AU and a surface temperature around 3500 K. It is thought to have evolved from an O-type main sequence star and will become a supernova in the next 100 000 years.