Alpha Pegasi (α Pegasi, abbreviated Alpha Peg, α Peg), formally named Markab /ˈmɑːrkæb/,^[11][12] is the third-brightest star in the constellation of Pegasus and one of the four stars in the asterism known as the Great Square of Pegasus.

Quick Facts Observation data Epoch J2000 Equinox J2000, Constellation ...

α Pegasi

Location of α Pegasi (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Pegasus
Right ascension	23h 04m 45.65345s[1]
Declination	+15° 12′ 18.9617″[1]
Apparent magnitude (V)	2.48[2]
Characteristics
Spectral type	A0 IV[3]
U−B color index	–0.06[2]
B−V color index	–0.04[2]
Variable type	suspected[4]
Astrometry
Radial velocity (Rv)	–2.2[5] km/s
Proper motion (μ)	RA: 60.40 ± 0.17[1] mas/yr Dec.: -41.30 ± 0.16[1] mas/yr
Parallax (π)	24.46 ± 0.19 mas[1]
Distance	133 ± 1 ly (40.9 ± 0.3 pc)
Absolute magnitude (MV)	–0.718[6]
Details
Mass	3.5[7] M☉
Radius	4.62±0.29[8] R☉
Luminosity	165[9] L☉
Surface gravity (log g)	3.98±0.25[8] cgs
Temperature	10,100±100[8] K
Metallicity [Fe/H]	−0.28[10] dex
Rotational velocity (v sin i)	130[8] km/s
Age	200[7] Myr
Other designations
Markab, Marchab, 54 Pegasi, HR 8781, BD+14°4926, HD 218045, SAO 108378, FK5 871, HIP 113963
Database references
SIMBAD	data

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Alpha Pegasi has a stellar classification of A0 IV, indicating that it is an A-type subgiant star that has exhausted the hydrogen at its core and has evolved beyond the main sequence. Its spectrum has also been classified as B9V^[13] and B9.5III.^[14]

It is rotating rapidly, with a projected rotational velocity of 130 km/s giving a lower bound on the azimuthal velocity along the star's equator. The effective temperature of the photosphere is about 10,000 K and the star has expanded to nearly five times the radius of the Sun, emitting 165 times as much energy as the sun.

α Pegasi (Latinised to Alpha Pegasi) is the star's Bayer designation. It bore the traditional name Markab (or Marchab), which derived from an Arabic word مركب markab "the saddle of the horse", or is mistranscription of Mankib, which itself comes from an Arabic phrase منكب الفرس Mankib al-Faras "(the Star of) the Shoulder (of the Constellation) of the Horse" for Beta Pegasi.

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[15] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN, which included Markab for this star.^[16]

In Chinese, 室宿 (Shì Xiù), meaning Encampment, refers to an asterism consisting α Pegasi and β Pegasi.^[17] Consequently, the Chinese name for α Pegasi itself is 室宿一 (Shì Xiù yī), "the First Star of Encampment".^[18]