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.
About this picture
NASA/Goddard Space Flight Center Scientific Visualization Studio. Gaia DR2: ESA/Gaia/DPAC. Constellation figures based on those developed for the IAU by Alan MacRobert of Sky and Telescope magazine (Roger Sinnott and Rick Fienberg). NASA's page (opens in a new tab).
The map is a composite of 1.7 billion catalogued stars, not a photograph from one place: it shows stars far too faint for the eye, and no weather, Moon or city light. It is drawn here in this chart's projection, with each star where it was in 2000; the fastest-moving bright star has shifted about a minute of arc since, far less than a pixel here.
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 is a red supergiant near the end of a short life, so large it would swallow the orbit of Jupiter.
Betelgeuse marks Orion's right shoulder (opens in a new tab) and blue-white Rigel his left foot. It is an ageing red supergiant, swollen so far (opens in a new tab) that if it took the Sun's place its outer surface would reach past the orbit of Jupiter.
It is young as stars go: NASA estimates (opens in a new tab) about 10 million years, against nearly 5 billion for the Sun. The more massive a star (opens in a new tab), the faster it runs through its fuel, and the biggest live only a few million years.
Its colour gives it away. Beside Rigel it looks plainly orange-red, a difference you can see from Earth (opens in a new tab): Rigel's surface is thousands of degrees hotter.
Sources for this section NASA Science, Discovering the Universe Through the Constellation Orion (opens in a new tab); NASA Science, Hubble Finds that Betelgeuse's Mysterious Dimming Is Due to a Traumatic Outburst (2020) (opens in a new tab); NASA Science, Star Basics (opens in a new tab)
The Great Dimming
In 2019 and 2020 Betelgeuse faded so much that people noticed by eye; a dust cloud was the likely cause.
Betelgeuse began to fade in October 2019, and by mid-February 2020 it had lost more than two-thirds of its brilliance (opens in a new tab), a change noticeable even to the naked eye. By April 2020 it was back to normal brightness.
Hubble's ultraviolet observations, led by Andrea Dupree of the Center for Astrophysics, pointed to an outburst (opens in a new tab): hot material welled up from a huge convection cell on the surface, travelled out through the star's atmosphere and cooled into dust, which blocked light from about a quarter of the star's surface.
The star already varies on its own. NASA describes (opens in a new tab) a cycle of about 420 days in which it expands and contracts, brightening and dimming, and the outburst came while the star was expanding in that cycle.
Keep in mind A variable star's change in brightness is real and lasts weeks or months. Twinkling is our own air, and lasts a fraction of a second.
Sources for this section NASA Science, Hubble Finds that Betelgeuse's Mysterious Dimming Is Due to a Traumatic Outburst (2020) (opens in a new tab)
Will it explode, and how far away is it?
Betelgeuse will end as a supernova one day, probably not soon, and its distance is still uncertain.
NASA (opens in a new tab) expects Betelgeuse to end its life as a supernova, but quotes Dupree that the chance of it happening any time soon is pretty small. Another NASA page (opens in a new tab) calls it a tiny chance in your lifetime and says that at its distance the explosion would be spectacular but not dangerous.
How far away is it? The sources disagree. NASA's 2020 Hubble article uses about 725 light-years (opens in a new tab), NASA's Orion page about 550 (opens in a new tab), and ESA's Hipparcos table (opens in a new tab) of the brightest stars leaves the distance blank. This page does not pick one.
Sources for this section NASA Science, Hubble Finds that Betelgeuse's Mysterious Dimming Is Due to a Traumatic Outburst (2020) (opens in a new tab); NASA Science, Discovering the Universe Through the Constellation Orion (opens in a new tab); ESA, Hipparcos: The 50 Brightest Stars (opens in a new tab)
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
- Astronomy NASA Science, Discovering the Universe Through the Constellation Orion (opens in a new tab) for its place in Orion, age, colour, future and a distance · checked 27 September 2026
- 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 cycle, its future and a distance · checked 27 September 2026
- Astronomy NASA Science, Star Basics (opens in a new tab) for why massive stars live short lives · checked 27 September 2026
- Astronomy ESA, Hipparcos: The 50 Brightest Stars (opens in a new tab) for the absent distance · checked 27 September 2026
