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Alpha Pegasi, 54 Pegasi

One of four bright stars that together form the Square of Pegasus, representing the body of the Winged Horse. Markab lies at the southwestern corner of the Square, and is designated Alpha Pegasi. Despite this 'Alpha' designation, Markab is in fact marginally less bright than Pegasus' Beta star, Scheat, which lies at the Square's northwestern corner.

The name Markab is variously interpreted as the Horse's 'saddle' or 'shoulder', and is also used for at least two other stars in the sky. One of these also lies in Pegasus: Tau Pegasi, more usually called Kerb, which lies within the bounds of the Square of Pegasus. The same name, or a close variant, is given to the quite unrelated Kappa Velorum, and sometimes also - due to confusion with Kappa Velorum - to k Puppis.

Markab is rapidly rotating star notable for the fact that it is in the process of emerging from the main sequence and beginning the process of expansion. It will ultimately evolve into a giant star, but at this point its boundary status means that it is variously classified as a dwarf, a subgiant or a giant. It is presently some 4.4 times the Sun's diameter, and more than 140 times as luminous, and its outer shell is expected to expand considerably in the future. Markab is blue-white in colour, lying on the boundary between the B-type blue and the A-type white spectral classifications.


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