Beta Orionis (Rigel)

β Orionis
beta Orionis (Rigel) Orion's left foot or leg, is the brightest star in the constellation. In fact the name 'Rigel' means 'Left Leg'.

The star is a binary (Struve 668) with a seventh magnitude visual companion 9.4" from the primary at a position angle of 202. The binary has a slight colour contrast, a bluish-white supergiant and blue companion.
    But due to the brightness of the primary you won't be able to resolve the binary with binoculars. It takes a large telescope to split the two.

However there is plenty here for the binoculars to absorb. With Rigel at the centre of your field of vision, you'll note four other bright stars, two to the northeast one to the north-northwest and one to the southwest: binoculars.
   To the north-northeast is tau Orionis (a binary with very faint companion) while more to the east of Rigel is 29 Orionis.
   Tau Orionis has a visual magnitude of 4.6, 29 Orionis is 4.1. This is exactly one-half a magnitude difference; do you notice the difference? Take your time, study the two for a while and see if you can tell that one is somewhat brighter than the other. This 'somewhat' is exactly half a magnitude.

As mentioned in the introduction, a difference of one magnitude means a brightness difference of two and a half times. A star with a half-magnitude difference has a brightness difference of 1.6. Thus tau Orionis is a bit more than one and a half times brighter than 29 Orionis.

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1998-2014 by Richard Dibon-Smith.