If Betelgeuse Explodes, It Will be So Bright You Could See It During the Day for a Year

Astronomers have been keeping a close eye on Betelgeuse for several months. 

Because of the unusual behavior of this star, located some 650 light-years away, many wonder if it's ready to go supernova.

Over the past few years, the red supergiant, already one of the brightest stars in the night sky – has dimmed dramatically between 2019 and 2020, becoming brighter than ever.

Since April this year, Betelgeuse has been shining about 160% of its normal brightness, sometimes shining brighter than other stars in the constellation Orion. Now it has risen from number ten to the seventh brightest star overall.

However, it is unlikely that it will explode as a supernova during our lifetime.

Albert Zyljstra, professor of astrophysics at the University of Manchester, has been trying to figure out what the Betelgeuse explosion would have looked like from Earth anyway, because, well, why not?

According to a new essay he wrote for The Conversation, is that it will be so spectacular that you can see it – or its erupted remnants, at least – during daylight for hours, and for a whole year.

For astronomers, the first indicator of Betelgeuse's explosion would actually be neutrino particles.

"We will first detect a rain of massless particles called neutrinos, which would be harmless to us" says Zyljstra. "After that, the brightness of this star will increase unexpectedly" he added.

At that stage, Betelgeuse will become as bright as, or even brighter than the full Moon. Then, it would gradually fade from this peak, but remain visible in daylight for eight to twelve months.

After sunset, however, is the time when the doomed star really shines.

"At night, you should be able to see it with the naked eye for the next year or two" Zyljstra wrote — quite a long time, in terms of eruptions.  "But after that, we'll never see it again" he added.

Given its relative proximity, it's fair to wonder whether Betelgeuse's end could prove dangerous to life on planet Earth.

Fortunately, Zyljstra says, there's nothing to worry about it. The radiation brought in by cosmic rays from a supernova at that distance "would be tiny compared to the other radiation we would receive for all but the closest supernova."

They reported that one such supernova about two to three million years ago, only 300 light-years away, irradiated iron as deep as the ocean floor but barely affected life on our pale blue dot.

However, 30 light years away we will face some big problems. At that distance, cosmic rays can destroy our ozone and cause mass extinctions. However, according to Zyljstra, this is extremely unlikely to happen "only 1/billion years".

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