If Betelgeuse Went Supernova, What Would We See From Earth?

Question posed by Robin.

Alpha Orionis, better known as Betelgeuse, is the second brightest star in the constellation Orion, and the eighth brightest star visible in the night sky. The star is located on the left shoulder of Orion, and is distinctly reddish in colour.

Betelgeuse is a red supergiant, and one of the largest stars visible in the sky. At approximately ten million years old it is reaching the end of its life, and such large stars don’t go quietly. With a mass nearing twenty times that of our own Sun*, Betelgeuse will go out with a bang – one of the biggest bangs in the universe; a supernova.

At only 640 light-years away, Betelgeuse is the closest candidate star to us for a potential supernova, and it could go off at any moment. It’s possible that it has already exploded and the light has not yet reached us. Scientists expect that Betelgeuse will go supernova some time in the next thousand years (I know that’s not very accurate, but predicting supernovae is a relatively young science).

But if Betelgeuse did go supernova within our lifetime…

… what would it look like from Earth?

It would brighten over the course of a fortnight until it outshone the Moon (though it would still be smaller in the sky). At this time, Betelgeuse’s supernova would be visible during the day, but would not, as some reports like to suggest, appear as large and as bright a ‘second sun’**. It would stay at that brightness for a couple of months before dimming rapidly (over a few days to a week). Eventually it will dim until it is impossible to see with the naked eye.

* If Betelgeuse were to suddenly appear in place of the Sun, we, on Earth, would be underneath its surface. By quite a way. Some estimates of Betelgeuse’s size have its surface as far out as the orbit of Jupiter. Check out the image below:

**  Sorry, Star Wars fans, we won’t feel like we’re on Tatooine!

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