Beta Pegasi (β Pegasi, abbreviated Beta Peg, β Peg), formally named Scheat /ˈʃiːæt/,^[11][12] is a red giant star and the second-brightest star (after Epsilon Pegasi) in the constellation of Pegasus. It forms the upper right corner of the Great Square of Pegasus,^[13] a prominent rectangular asterism.

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

Beta Pegasi

Location of β Pegasi (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Pegasus
Right ascension	23h 03m 46.45746s[1]
Declination	+28° 04′ 58.0336″[1]
Apparent magnitude (V)	2.42[2] (2.31 – 2.74)[3]
Characteristics
Spectral type	M2.5II–IIIe[4]
U−B color index	+1.96[2]
B−V color index	+1.67[2]
Variable type	Semi-regular[5]
Astrometry
Radial velocity (Rv)	+8.7[6] km/s
Proper motion (μ)	RA: +187.65[1] mas/yr Dec.: +136.93[1] mas/yr
Parallax (π)	16.64 ± 0.15 mas[1]
Distance	196 ± 2 ly (60.1 ± 0.5 pc)
Absolute magnitude (MV)	−1.41[7]
Details
Mass	2.1[8] M☉
Radius	95 R☉
Surface gravity (log g)	1.20[9] cgs
Temperature	3,689[9] K
Metallicity [Fe/H]	−0.11[9] dex
Rotational velocity (v sin i)	9.7[10] km/s
Other designations
Scheat, 53 Pegasi, HR 8775, BD+27°4480, HD 217906, SAO 90981, FK5 870, HIP 113881[4]
Database references
SIMBAD	data

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β Pegasi (Latinised to Beta Pegasi) is the star's Bayer designation.

It bore the traditional name of Scheat, a name that had also been used for Delta Aquarii. The name was derived from the Arabic Al Sā'id "the upper arm", or from Sa'd.^[13] In 2016, the International Astronomical Union organised a Working Group on Star Names (WGSN)^[14] to catalog and standardise proper names for stars. The WGSN's first bulletin of July 2016^[15] included a table of the first two batches of names approved by the WGSN; which included Scheat for this star (the name Skat was later approved for Delta Aquarii^[12]).

In Chinese, 室宿 (Shì Xiù), meaning Encampment, refers to an asterism consisting β Pegasi and α Pegasi.^[16] Consequently, the Chinese name for β Pegasi itself is 室宿二 (Shì Xiù èr), "the Second Star of Encampment".^[17]

Based upon parallax measurements, Beta Pegasi is located about 196 light-years (60 parsecs) from the Sun.^[1] It is unusual among bright stars in having a relatively cool surface temperature compared to stars like the Sun. This star has a stellar classification of M2.3 II–III,^[4] which indicates the spectrum has characteristics partway between a bright giant and a giant star. It has expanded until it is some 95 times as large, and has a total luminosity of 1,500 times that of the Sun. The effective temperature of the star's outer envelope is about 3,700 K,^[9] giving the star the characteristic orange-red hue of an M-type star.^[19] The photosphere is sufficiently cool for molecules of titanium oxide to form.^[20]

Beta Pegasi is a semi-regular variable with a period of 43.3 days^[5] and a brightness that varies from magnitude +2.31 to +2.74 (averaging 2.42).^[3] It is losing mass at a rate at or below 10⁻⁸ times the Sun's mass per year, which is creating an expanding shell of gas and dust with a radius of about 3,500 times the Sun's radius (16 astronomical units).^[21]