Alpha Mensae

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Alpha Mensae
Observational Data
Designation α Men
Right ascension 06h 10m 14.4741s[1][2]
Declination -74° 45′ 10.9635″[1][2]
Constellation Mensa
Type of object Main sequence star
Magnitude Apparent Mag: +5.08[3]
Absolute Mag: +5.05[3]
Distance from Earth 33.26 ly[3]
Radial velocity 36.15±0.13 km/s[1][2]
Proper motion RA: 121.203 mas/yr[1][2]
Dec.: -212.100 mas/yr[1][2]
Parallax 97.8983±0.0719 mas[1][2]

Alpha Mensae (α Men, HIP29271) is a main sequence star in the constellation of Mensa.[3] With an apprent magnitude of +5.08, it is in fact the brightest star in Mensa, the next brightest is Gamma Mensae.[3] It is noted for its high proper motion (how position of the star in the sky changes) compared to most stars. The star is just about bright enough to be seen with the naked eye in good conditions and its low declination means is best observed in the southern hemisphere. The star's spectral class of G5V means it appears yellow/white similar to the Sun. It was one of the top 100 stars for NASA's Terrestrial Planet Finder (TPF) mission before it was cancelled.[4] No planetary bodies have been detected around the star by other missions.

With a distance of 33.26 light years, Alpha Mensae is one of the closer stars to Earth.[3] It is thought to have a mass of 0.91 solar masses, though other put it higher at 1.1 solar masses.[5] Its diameter is also slightly smaller at 84-91% than that of the Sun.[4][6][7] The star was thought to possess a luminosity of around 80% that of the Sun, though more recent measurements place it higher at 93%.[3][5] The star has a slightly greater metallicity than the Sun (amount of elements heavier than hydrogen and helium in the star).[8]

The star is a slow rotator, meaning it rotates once every 32 days.[5] The star has a B-V Colour Index of 0.71 and a temperature of 5,533 Kelvin.


  1. 1.0 1.1 1.2 1.3 1.4 1.5 Alpha Mensae. Simbad Astronomical Database. Retrieved on 2019-07-05.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Gaia Colaboration. VizieR Online Data Catalog: Gaia DR2 (Gaia Collaboration, 2018). (2018). VizieR Online Data Catalog. Bibcode:2018yCat.1345....0G
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Alpha Mensae. Retrieved on 2019-07-05.
  4. 4.0 4.1 Alpha Mensae. Retrieved on 2019-07-05.
  5. 5.0 5.1 5.2 Jim Kaler (2015-06-16). Alpha Mensae. Stars. Retrieved on 2019-07-05.
  6. Perrin, M.; Karoji, H. (1987). "Stellar radius determination from IRAS 12 mu.m fluxes". Astronomy and Astrophysics 172 (1-2): 235-240. Bibcode1987A&A...172..235P. 
  7. Johnson, H.; Wright, C. (1983). "Predicted infrared brightness of stars within 25 parsecs of the sun". The Astrophysical Journal Supplement Series 53: 643. doi:10.1086/190905. Bibcode1983ApJS...53..643J. 
  8. Cayrel de Strobel, G.; Hauck, B.; Francois, O. (1992). "A catalogue of Fe/H determinations - 1991 edition". Astronomy and Astrophysics Supplement Series 95: 273-336. Bibcode1992A&AS...95..273C.