Betelgeuse

Betelgeuse is a red supergiant of spectral type M1-M2Ia-Iab, one of the largest stars visible to the naked eye. Located about 650 light-years from Earth, it marks the upper left shoulder of Orion. Betelgeuse is roughly 700-1,000 times the diameter of the Sun — if placed at the center of our solar system, its surface would extend beyond the orbit of Jupiter. It is a semiregular variable star, fluctuating between about magnitude 0.0 and 1.6 over periods of roughly 400 days. Its luminosity is about 100,000 times that of the Sun.

Betelgeuse is instantly recognizable as the distinctly red-orange star at Orion's upper left shoulder. Its color contrast with blue-white Rigel at the opposite corner of Orion is one of the most striking sights in the sky. Monitoring Betelgeuse's brightness changes relative to nearby reference stars (Aldebaran, Pollux, Procyon) is an excellent visual variable star project. Best observed from November through March. In late 2019-early 2020, Betelgeuse underwent an unprecedented dimming event that sparked worldwide attention.

The name Betelgeuse likely derives from the Arabic 'Yad al-Jawza' meaning 'hand of the central one,' though the precise etymology is debated. It was among the first stars to have its angular diameter measured, by Albert Michelson and Francis Pease using the Mount Wilson 100-inch telescope's interferometer in 1920. Its variable nature was first noted by Sir John Herschel in 1836.