Regulus

Regulus A/B/C

Regulus is located at the lower right on this map of the constellation.
Observation data Epoch J2000      Equinox J2000
Constellation	Leo
Right ascension	A: 10h 08 min 22.3s BC: 10h 08 min 12.8/14s
Declination	A: +11° 58' 02" BC: +11° 59' 48"
Apparent magnitude (V)	1.35/8.14/13.5
Characteristics
Spectral type	B7 V/K1-2 V/M5 V
U-B color index	−0.36/0.54
B-V color index	−0.11/0.87
Variable type	Slightly
Astrometry
Radial velocity (Rv)	+5.9 km/s
Proper motion (μ)	RA: 249 mas/yr Dec.: 2 mas/yr
Parallax (π)	42.09 ± 0.79 mas
Distance	77 ± 1 ly (23.8 ± 0.4 pc)
Absolute magnitude (MV)	−0.52/4.2/9.5
Details
Mass	3.5/0.8/0.2 M☉
Radius	3.15–4.15/0.5/? R☉
Luminosity	150/0.31 L☉
Temperature	10,300–15,400/? K
Rotation	315 km/s. (15.9 hours)/?
Age	5 × 107 years
Other designations
Alpha Leonis, 32 Leo, Cor Leonis, Basilicus, Lion’s Heart, Rex, Kalb al Asad, Kabeleced, GJ 9316, HR 3982, BD +12° 2149/2147, HD 87901/87884, GCTP 2384.00, LTT 12716/12714, SAO 98967/98966, FK5 380, HIP 49669, TD1 14585.
Database references
SIMBAD	data

Regulus (α Leo / α Leonis / Alpha Leonis) is the brightest star in the constellation Leo and one of the brightest stars in the nighttime sky, and lies approximately 77.5 light years from Earth. Regulus is a multiple star system composed of four stars which are organised into two pairs. The spectroscopic binary Regulus A consists of a blue-white main sequence star and its companion which has not yet been directly observed, but is probably a white dwarf star.^[1] Located further away is the pair Regulus B and Regulus C, which are dim main-sequence stars.

Observations

Of the brightest stars in the sky, Regulus is closest to the ecliptic, and is regularly occulted by the Moon. Occultations by the planets Mercury and Venus are also possible but rare. The last occultation of Regulus by a planet was on July 7, 1959, by Venus. The next will occur on October 1, 2044, also by Venus. Other planets will not occult Regulus over the next few millennia because of their node positions.

The Sun makes its closest approach to Regulus around August 23 of each year. For most Earth observers, the heliacal rising of Regulus occurs in the first week of September. Every 8 years, Venus passes Regulus around the time of the star's heliacal rising, most recently in 2006.

Regulus has about 3.5 times the Sun’s mass and is a young star of only a few hundred million years. It is spinning extremely rapidly, with a rotation period of only 15.9 hours, which causes it to have a highly oblate shape.^[2] This results in so-called gravity darkening: the photosphere at Regulus' poles is considerably hotter, and five times brighter per unit surface area, than its equatorial region. If it were rotating only 16% faster, centripetal force would overcome gravity and the star would tear itself apart.

Visibility

Regulus A is one of the brightest stars in the night sky with an impressive apparent magnitude. Regulus B is a smaller dwarf star of spectral type K2 which would make it significantly dimmer than A. The final companion, Regulus C, is a small red star and the faintest of the three stars which have been directly observed. Regulus A is itself a spectroscopic binary: the secondary star has not yet been directly observed as it is much fainter than the primary. The BC pair lies at an angular distance of 177 arc-seconds from Regulus A, making them visible in amateur telescopes.

System

Regulus is a multiple star system consisting of four stars. Regulus A is a binary star consisting of a blue-white main sequence star of spectral type B7V which is orbited by a star of at least 0.3 solar masses which is probably a white dwarf. The two stars take approximately 40 days to complete an orbit around their common centre of mass. At a distance of around 4,200 AU from Regulus A is another pair of stars, designated Regulus B and Regulus C. The companion pair have an orbital period of 2,000 years and are separated by about 100 AU.

Etymology and Cultural Associations

Rēgulus is Latin for 'prince' or 'little king'. The Greek variant Basiliscus is also used. It is known as Qalb Al Asad, from the Arabic قلب لأسد or Qalb[u] Al-´asad, meaning 'the heart of the lion'. This phrase is sometimes approximated as Kabelaced and translates into Latin as Cor Leōnis. It is known in Chinese as 轩辕十四, the Fourteenth Star of Xuanyuan, the Yellow Emperor. In Hindu astronomy, Regulus corresponds to the Nakshatra Magha.

Persian astrologers around 3000 BC knew Regulus as Venant, one of the four 'royal stars'.^{[citation needed]} It was one of the fifteen Behenian stars known to medieval astrologers, associated with granite, mugwort, and the kabbalistic symbol .

Regulus

See also

• Leo constellation
• Table of stars with Bayer designations
• Regulus in fiction

References

1. ^ Gies, D.R. et al. (2008). "A Spectroscopic Orbit for Regulus". The Astrophysical Journal 682 (2): L117–L120. doi:10.1086/591148. Bibcode: 2008ApJ...682L.117G. 
2. ^ McAlister, H. A., ten Brummelaar, T. A., et al. (2005). "First Results from the CHARA Array. I. An Interferometric and Spectroscopic Study of the Fast Rotator Alpha Leonis (Regulus).". The Astrophysical Journal 628: 439–452. doi:10.1086/430730. 

• Fred Schaaf, “Horrorfications of the Lion’s heart,” Sky & Telescope, April 2006.

External links

• Portrait of a Star on the Edge
• Egg-Shaped Regulus is Spinning Fast
• Regulus as Astronomy Picture of the Day of 19th june 2006
• "Regulus 3". SolStation. http://www.solstation.com/stars2/regulus3.htm. Retrieved December 1 2005.