The wobblings of Betelgeuse

You’ve probably heard in the mainstream media that there’s a star in Orion that’s gone dim over the last couple of months and might "go supernova". Maybe, but don’t hold your breath.

Betelgeuse is a red giant star in the constellation of Orion, one of the shoulders of the Hunter. Of course, in the Southern Hemisphere, we see it "upside down", so Betelgeuse is the lowest bright star in the constellation. Just now, from Southern Australia, Orion is rising in the East after sunset.

A red giant is a huge star. If it were transferred to where our sun is, the Earth would be inside the star itself. So would Mars and – nearly – Jupiter. Only large stars can result in supernovas, but this one is plenty big enough.

It’s also true that it’s gone suddenly and significantly dimmer over the past few months. Betelgeuse was until recently one of the top 10 brightest stars in the sky. Now it’d struggle to make the top 20 list.

However, it's also variable, changing brightness on a semi-regular basis. So, is this sudden and significant dimming just part of its regular ups and downs, or is it actually in its death throes? We don’t know – we haven’t been able to study enough supernovas to learn what they do at the end.

A supernova is pretty much the biggest explosion the universe can muster, unless you’re counting the Big Bang. Betelgeuse is not far away either - about 600 light years away from the Earth. So if (or maybe when?) it goes, astronomers think it’ll be so bright you could see it during the day. It’ll be awesome, but we will be quite safe.

In the media it sounds as though it’ll be some time this week. You’re more likely to die of old age first. Realistically, it’ll probably go in the next million years or so, with the occasional splutter now and again beforehand.

The photos here were taken three years apart. I've arrowed Betelgeuse and Alhena in both, and you can see that last year (left), Betelgeuse outshone Alhena by miles. This year's photo (right), not so much!