α Sagittarii

Alpha Sagittarii is Rukbat, the archer's knee: binoculars. It's three binocular fields southeast of epsilon Sagittarii.

There are fifteen stars in Sagittarius brighter than alpha. While it isn't clear why Bayer labelled the star alpha, two possibilities have been suggested. First, the star may have been much brighter in antiquity, when Ptolemy first wrote about it, and Bayer just followed suit. Secondly, since neither Ptolomy nor Bayer could actually see the star, information about the star's brightness was simply wrong.

Since the beta stars, also in this field, are misrepresented as well as being brighter than they are, the second possibility may be more likely.

These unrelated stars, beta1 and beta2, are named ‘Arkab Prior’ and ‘Arkab Posterior’, respectively the front and the back of the leg.

Beta1 is a fairly wide binary (DUN 226): 4.0, 7.2; 76º, 28.7", a blue primary and white companion.

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