When Betelgeuse goes supernova, what will it look like from Earth?

If you stargaze on a clear winter night, it’s hard to miss the

constellation Orion the Hunter, with his shield in one arm and the other

arm stretched high to the heavens. A bright red dot called Betelgeuse

marks Orion’s shoulder, and this star's strange dimming has captivated

skygazers for thousands of years. Aboriginal Australians may have even

worked it into their oral histories.

Today, astronomers know that Betelgeuse varies in brightness because

it’s a dying, red supergiant star with a diameter some 700 times larger

than our Sun. Someday, the star will explode as a supernova and give

humanity a celestial show before disappearing from our night sky

forever.

That eventual explosion explains why astronomers got excited when

Betelgeuse started dimming dramatically in 2019. The 11th-brightest star

dropped in magnitude two-and-a-half-fold. Could Betelgeuse have reached

the end of its life? While unlikely, the idea of a supernova appearing

in Earth’s skies caught the public’s attention.

And now new simulations are giving astronomers a more precise idea of

what humans will see when Betelgeuse does eventually explode sometime in

the next 100,000 years.Supernova seen from Earth

With all the speculation about what a Betelgeuse supernova would look

like from Earth, University of California, Santa Barbara, astronomer

Andy Howell got tired of the back-of-the-envelope calculations. He put

the problem to a pair of UCSB graduate students, Jared Goldberg and Evan

Bauer, who created more precise simulations of the star’s dying days.

The astronomers say there’s still uncertainty over how the supernova

would play out, but they were able to augment their accuracy using

observations taken during Supernova 1987A, the closest known star to

explode in centuries.

Life on Earth will be unharmed. But that doesn’t mean it will go

unnoticed. Goldberg and Bauer found that when Betelgeuse explodes, it

will shine as bright as the half-Moon — nine times fainter than the full

Moon — for more than three months.

“All this brightness would be concentrated into one point,” Howell says.

“So it would be this incredibly intense beacon in the sky that would

cast shadows at night, and that you could see during the daytime.

Everyone all over the world would be curious about it, because it would

be unavoidable.”

Humans would be able to see the supernova in the daytime sky for roughly

a year, he says. And it would be visible at night with the naked eye

for several years, as the supernova aftermath dims.

“By the time it fades completely, Orion will be missing its left

shoulder,” adds Sarafina Nance, a University of California, Berkeley,

graduate student who’s published several studies of Betelgeuse.