Markab / Alpha Pegasi / HD 218045
Distance: 139.552 ly
Abs (app) mag = -0.67 (2.49)
Class: B9 III
Radius: 3.81 Rsun
Four
stars make the Great Square in the
Pegasus constelation, Markab (
Alpha) placed on the southwestern corner, Scheat (
Beta) at the northwestern,
Algenib (
Gamma) at the southeastern, and
Alpheratz (Alpha Andromedae) at the northeastern, this last star linking the Winged Horse to
Andromeda.
Markab's name comes from an
Arabic phrase meaning "the horse's shoulder". It is a relatively hot (class B, though at the cool end) giant. Its distance of aproximatelly 140 light years leads to a total luminosity 205 times that of the Sun (including some invisible ultraviolet).
Markab has just begun to die. If hydrogen fusion has not already ceased in its
core, it is very close. The star is in a sense clinging to its lifeline on the hydrogen-fusing normal "main sequence" of stars and is about to leap into the
abyss, in which it will quickly
expand, slow its
rotation, and become a much cooler orange giant.
It will then brighten to many times its current luminosity to
die finally as a massive
white dwarf like
Sirius B. Some stars are remarkable for their chemical compositions, others for their multiplicity, yet others for strange variability. Though there is some evidence from Markab's motion for a small stellar companion, the star is famed for none of these. It is in fact noted for its very
normality, behaving quite like it should. Such
normalcy is extremely important in stellar
astronomy, as it provides a bedrock
standard against which to measure the
odder members of the stellar
zoo. Of the 100 publications in which Markab has been mentioned in the past 15 years, nearly all use it as such a base.
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