Great Dimming2019–2020from magnitude ≈ 0.5 to 1.7[1]
Supernovaprobably within 100 000 yearsnot imminent[1]
CompanionSiwarhanamed by the IAU on 22 September 2025[1]
About the image. Drawn as a mottled red supergiant, with the colour of a star near 3 600–3 800 K (3 530 °C). Its surface really is patchy, but the pattern drawn here is imagined.
Betelgeuse is the reddish star at Orion’s shoulder, one of the brightest in the night sky. It is a red supergiant: a star many times heavier than the Sun, now swollen to somewhere between 640 and 760 times its width. At its distance of roughly 400 to 550 light-years, it is close enough that astronomers can resolve its surface.
The Great Dimming
In late 2019 Betelgeuse began to fade. By mid-February 2020 it had dropped from about magnitude 0.5 to 1.7, visibly dimmer to anyone looking at Orion, and people wondered if it was about to explode. It wasn’t. Hubble observations suggested that the star had thrown off a burst of hot material, which cooled into a cloud of dust and blocked light from part of its surface. Infrared measurements showed that the star’s actual power output had barely changed.
A companion
For years astronomers suspected that a small companion star orbits Betelgeuse. The evidence is still indirect, and the companion is not yet fully confirmed to be gravitationally bound, but it is likely. On 22 September 2025 the International Astronomical Union approved a name for it: Siwarha.
When will it explode?
Betelgeuse will end as a supernova, probably within the next 100 000 years. That is soon by the standards of stars, but not something anyone should expect to see. When it does go, Orion will lose its shoulder.
To scale · radius, Sun = 1Sun: 1.00 · Betelgeuse: 764Upper radius estimate (Joyce et al. 2020).
How hot is it?
Earth (average)288 K · 15 °C
Water boils373 K · 100 °C
Venus surface737 K · 464 °C
Iron melts1 811 K · 1 540 °C
Sun's surface5 772 K · 5 500 °C
Betelgeuse3 780 K · 3 510 °C
Betelgeuse: surface temperature. Logarithmic scale from 100 K to 10 000 K. Reference values: NASA, IAU.
How long to get there?
Betelgeuse is about 500 light-years away (middle of the 400–550 light-year range).
Light299 792 km/s500 years
Breakthrough Starshotplanned light sail, 20% of light speed2 500 years
Parker Solar Probefastest spacecraft so far, 192 km/s780 708 years
Voyager 1leaving the Solar System, 17 km/s8.8 million years
At Voyager 1's speed the trip would take about 110 218 human lifetimes of 80 years. Bars are on a logarithmic scale. Speeds: NASA, Breakthrough Initiatives.
Gallery
Artist's impressions rendered from the same model as the view at the top of this page.
Timeline
2019The Great Dimming begins.
2020Brightness bottoms out in February; dust from ejected material is the leading explanation.
2022Hubble data point to a surface mass ejection.
2025Its companion star is named Siwarha.
Questions people ask
When will Betelgeuse explode?
Probably within the next 100 000 years. It is not expected to happen soon.
Why did Betelgeuse dim in 2019?
It threw off hot material that cooled into dust and blocked part of its light. Its actual power output barely changed.
Does Betelgeuse have a companion?
Probably. A small companion, named Siwarha in 2025, is likely but not yet fully confirmed to be bound to it.