Popular Astronomy

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Guide to Betelgeuse (Alpha Orionis)

A bright variable star that shows slow changes over the course of several years.

Betelgeuse is a red giant star that is in the final stages of its evolution. Currently it shows slow semi-regular brightness changes with a range of up to half a magnitude. The brightness changes are related to pulsations in its outer layers. However, the appearance and disappearance of large convection cells on its surface may also influence the brightness changes seen.

Although some sensational news stories may give you the impression that Betelgeuse is about to go supernova, the chances of this are very small and the supernova will most likely not occur for many thousands of years.

Extreme brightness range 0.4 - 1.3
More typical range 0.4 - 0.8
Period of variation Possible around 4 years (although the GCVS gives a longer value of 2070 days)
Frequency of observation Worth checking once or twice each month
Observe using Naked Eye
Visibility Can be observed from mid August to late April

The chart below shows the comparison stars for Betelgeuse.

When observing Betelgeuse take care to ensure, whenever possible that the comparison stars used are at a similar altitude to Betelgeuse. Otherwise dimming by haze can affect the accuracy of your brightness estimates. For this reason, Rigel should not be used as a comparison star.