Science & history · Star guide
Betelgeuse, Orion's red supergiant
Betelgeuse is the reddish star at Orion's shoulder: a red supergiant so large that, put in place of the Sun, its surface would reach beyond the orbit of Jupiter. In 2019 and 2020 it faded so much that people noticed with the naked eye.
How to spot it: The reddish star at Orion's shoulder, opposite blue-white Rigel. Source (opens in a new tab)
What you are looking at
Betelgeuse marks Orion's right shoulder (opens in a new tab), and Rigel his left foot. It is an ageing red supergiant, swollen so far (opens in a new tab) that its surface would extend past Jupiter's orbit if it sat where the Sun is. Its colour is the easiest clue: it is plainly orange-red beside blue-white Rigel.
The Great Dimming
Beginning in October 2019, Betelgeuse lost more than two-thirds of its brilliance (opens in a new tab) by mid-February 2020, and was back to normal by April. Hubble's observations pointed to an outburst: hot material thrown out of the star cooled into a dust cloud that blocked part of its light.
Will it explode?
One day, yes: NASA (opens in a new tab) expects it to end as a supernova. But the chance of that happening any time soon is small.
How far away?
Honestly, not precisely known. NASA's 2020 article uses about 725 light-years (opens in a new tab), while ESA's Hipparcos table (opens in a new tab) of the brightest stars leaves its distance blank. It is a variable star in that table.
In another tradition
In Vedic astrology Betelgeuse is the star of Ardra, the sixth lunar mansion.
Where on Earth, and when
It rises from anywhere north of about 83°S.
North of about 83°N, it never sets.
It climbs at least 20° high, the finder's threshold for a suggestion, from latitudes between 63°S and 77°N.
It is highest in the evening sky, at about 9 p.m. local time, in mid-February, from either hemisphere, wherever it rises. With daylight saving time, that is nearer 10 p.m. on the clock.
Worked out by this site from the Bright Star Catalogue, for a flat, clear horizon. Hills, buildings, haze and city light all cut into this; the air also lifts objects near the horizon by about half a degree. For your own place and night, use the sky finder.
Sources
- History Ian Ridpath, Star Tales: Orion (opens in a new tab) for its place in Orion
- Astronomy NASA Science, Hubble Finds that Betelgeuse's Mysterious Dimming Is Due to a Traumatic Outburst (2020) (opens in a new tab) for size, the Great Dimming, its future and a distance
- Astronomy ESA, Hipparcos: The 50 Brightest Stars (opens in a new tab) for its variability and the absent distance