Alpha Orionis (Betelgeuse)

α Orionis
Alpha Orionis has perhaps the most famous star name in the heavens, Betelgeuse, which is a distortion of the Arabic for "Armpit of the Central One".

     There is some confusion about just how ‘Betelgeuse’ is pronounced. Some declare that the first syllable must rhyme with 'metal'. Others adamantly proclaim that it should sound like 'beetle'.
     The last syllable -- it is also argued by some -- should sound just like 'juice'. Not a bit of it, say others, who opt for a zed (or zee) sound. The truth is, nobody knows, and you can jolly well pronounce it any way you like!

The star is a red supergiant, the brightest variable star in the heavens. It may go from a brightness of 0.3 (nearly as bright as Rigel) to 0.9 (about the same brightness as Aldebaran, alpha Taurus, to the northeast. These two stars, then, are excellent guides by which one might make visual comparisons to see just what Betelgeuse is up to.

Since antiquity the star has formed the right shoulder (or armpit) of Orion. That is, except briefly, when Johann Bayer published his star catalogue in 1603. Bayer turned Orion around, having The Hunter's back to the viewer, which complicated everybody's enjoyment of the skies. Suddenly Betelgeuse stood for Orion's left shoulder/armpit and Rigel was Orion's right foot.

Others promptly busied themselves turning Orion around, and it wasn't long before he was restored to his traditional aspect, attacking Taurus face on.

In binoculars, if you place Betelgeuse at the centre of your field of vision then you will see two fairly bright stars in the same area, one to the northeast and one to the southwest: binoculars.
   The star to the northeast is mu Orionis, while to the southwest is 52 Orionis. Both are binaries but you are not expected to be able to split them with binoculars.

With these three stars in your field of vision you can begin to judge the relative visual brightness of stars. Betelgeuse is a very bright 0.45 while mu Orionis is 4.1 (actually this is the combined value of its two components). The combined visual magnitude* of the two components of 52 Orionis is 5.3.

    (*If the term ‘visual magnitude’ has you a bit confused, take a brief moment to read these short remarks).

Continue with your discovery of Orion by clicking on any of the other orange-coloured stars or deep sky objects.

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© 1998-2014 by Richard Dibon-Smith.