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‘Something is not quite right’ when you look to the sky

19 January, 2020 - 21:00
Astronomer, Neil Norman  Picture: SARAH LUCY BROWN

Astronomer, Neil Norman Picture: SARAH LUCY BROWN

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It’s been plastered over the news that the red giant star, Betelgeuse in Orion may be on the verge of going supernova on us as it ends its life, says astronomer Neil Norman, of Hadleigh.

A look at the sky chart shows us that Betelgeuse is equal in brightness to Rigel in Orion and a tad brighter than Aldeberan in Taurus, but if you look up tonight you will see that this is not the case - it has dimmed very dramatically.

It began dimming in October last year and it is very obvious to a regular observer of the star that something is not quite right.

Is there any need for concern?

Well, Betelgeuse is a giant red star that has burned out its hydrogen and is now burning its reserves of helium up at a staggering rate, but it doesn't mean that it will go boom anytime soon. As much as 100,000 years is the scientific thought, but even if these figures are drastically wrong, the chances of a supernova in the next century are slim.

It has a mass 20 times that of our own Sun and if Betelgeuse was placed in our own Solar system it would reach out to the orbit of Jupiter. Earth would actually be inside of the star and obviously this would not do us any favours.

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Its distance from us is somewhere in the region of 650 light years, meaning the light reaching us today began its journey from the star in around A.D 1370, but for a star to explode and cause the Earth damage, it would need to be much closer, more like 300 light years from us before any noticeable change would affect us.

When it finally does blow, it will become as bright as the full Moon.

That will be a double-edged sword for astronomers, because the excitement of a nearby supernova will be squashed by the fact the sky will be lit up dramatically affecting other observational work.

But Betelgeuse is not acting out of the ordinary, it is a well known variable star: it dims and brightens over well observed periods of time. When it expands its shells of outer atmosphere it brightens and when these shrink back through gravity it dims. This happens over a period of 400 days and is well known after centuries of observations.

The upper layers are convective: hot gas deep inside rises, gets to the surface, cools off, and sinks again. The hotter gas is brighter, so this affects the stars luminosity. Betelgeuse is a monster as stars go and can expel gas plumes as large as our entire solar system.

So, no need to read the headlines and panic. Betelgeuse does this all the time, but it is interesting to watch and document with pictures, sketches or even your comparison estimates in its brightness with Aldebaran.

Neil Norman, a Fellow of The Royal Astronomical Society, is writing for us each month, giving amateur stargazers suggestions of what to look out for in the skies over Suffolk in 2020.

MORE: 7 times you need to look to the sky in 2020

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