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Alpha Pegasi (α Pegasi, abbreviated Alpha Peg, α Peg), formally named Markab /ˈmɑːrkæb/,[8][9] 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.

Alpha Pegasi
Diagram showing star positions and boundaries of the Pegasus constellation and its surroundings
Cercle rouge 100%.svg
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]
Spectral type A0 IV[3]
U−B color index –0.06[2]
B−V color index –0.04[2]
Variable type suspected[4]
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[1] mas
Distance133 ± 1 ly
(40.9 ± 0.3 pc)
Radius4.72 ± 0.14[6] R
Surface gravity (log g)3.51 ± 0.03[6] cgs
Temperature9,765 ± 63[6] K
Metallicity [Fe/H]−0.02 ± 0.10[6] dex
Rotational velocity (v sin i)125[7] km/s
Other designations
Markab, Marchab, 54 Pegasi, HR 8781, BD +14°4926, HD 218045, SAO 108378, FK5 871, HIP 113963.
Database references

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.

Markab 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. It is rotating rapidly, with a projected rotational velocity of 125 km/s giving a lower bound on the azimuthal velocity along the star's equator. The effective temperature of the photosphere is nearly 10,000 K and the star has expanded to nearly five times the radius of the Sun.


In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[10] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[11] included a table of the first two batches of names approved by the WGSN, which included Markab for this star.

In Chinese, 室宿 (Shì Xiù), meaning Encampment, refers to an asterism consisting α Pegasi and β Pegasi.[12] Consequently, the Chinese name for α Pegasi itself is 室宿一 (Shì Xiù yī), "the First Star of Encampment".[13]


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
  2. ^ a b c Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
  3. ^ Abt, Helmut A.; Morrell, Nidia I. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". Astrophysical Journal Supplement. 99: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.
  4. ^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  5. ^ Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35), Bibcode:1999VeARI..35....1W
  6. ^ a b c d Fitzpatrick, E. L.; Massa, D. (March 2005), "Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry", The Astronomical Journal, 129 (3): 1642–1662, arXiv:astro-ph/0412542, Bibcode:2005AJ....129.1642F, doi:10.1086/427855
  7. ^ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590
  8. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  9. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  10. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  11. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  12. ^ ‹See Tfd›(in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  13. ^ ‹See Tfd›(in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.