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Alpha Pegasi, 54 Pegasi

Proper NameMarkab
Bayer DesignationAlpha Pegasi
Flamsteed Number54 Pegasi
HR (BSC)8781
Right Ascension23h 4m 46s
Declination+15° 12' 19"
Distance133 light years
41 parsecs
MagnitudeApparent: +2.5
Absolute: -0.6
Spectral ClassB9V blue main sequence star
Optimum VisibilitySeptember
NotesThough designated Alpha Pegasi, Markab is not the brightest star in Pegasus (both Enif and Scheat are marginally brighter). Though presently blue-white in colour, the star is in the later stages of its evolution, and will eventually cool and expand into a red giant.

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 Salm or 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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