Regulus
Regulus (α Leo, α Leonis, Alpha
Leonis) is the brightest star in the constellation
Leo and one of the brightest
stars in the night sky, lying
approximately 79 light years from Earth.[1]
Regulus is a multiple star system composed of four stars that are organized 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.[7]
Located farther 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, as are occultations by asteroids.
The last occultation of Regulus by a planet was on July 7, 1959, by Venus.[8]
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.
Regulus is expected to be occulted
by the asteroid 163 Erigone on March 20, 2014.[9]
This event will be visible along a path about 40 miles wide from New York City
to Oswego in the United States, and extending approximately northwest into
Canada on a track that includes Belleville and North Bay, Ontario.[10]
An occultation of Regulus by the
asteroid 166 Rhodope was observed by 12 observers from Portugal, Spain, Italy,
and Greece on 2005-10-19. Details are at http://www.euraster.net/results/2005/index.html#1019-166
Although best seen in the evening in
northern hemisphere in late winter and spring, Regulus can be found at some
time of night throughout the year except for about a month on either side of
August 22, when the sun is too near.[11]
Regulus passes through SOHO's LASCO C3 every August.[12]
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.
The primary of Regulus A 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.[13]
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, the star's gravity would provide insufficient
centripetal force to hold it together, and it would tear itself apart.
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. Given the extremely distorted shape of the primary, the
relative orbital motion may be notably altered with respect to the two-body
purely Keplerian
scenario because of non-negligible long-term orbital perturbations affecting,
for example, its orbital period. In other words, the third Kepler law, which holds exactly only for
two pointlike masses, would be no longer valid because of the highly distorted
shape of the primary.
At a distance of around 4,200 AU[citation needed] from Regulus A is a binary star system that shares a
common proper motion. Designated Regulus B and Regulus C, the Henry Draper Catalogue number for this pair is HD 87884. The first is a K2V star,
while the companion is approximately M4V.[13]
The companion pair has an orbital period of 2,000 years and is separated by
about 100 AU.[citation needed]
Visibility
The Regulus system as a whole is the
twenty-first brightest star in the night sky with an apparent magnitude of +1.35. The light output is dominated by Regulus A.
Regulus B, if seen in isolation, would be a binocular object of magnitude +8.1,
and its companion, Regulus C, the faintest of the three stars that has been
directly observed, would require a substantial telescope to be seen, at
magnitude +13.5. 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[citation needed].
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 الأسد, 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 ("the bountiful").
Persian astrologers around 3000 BC
knew Regulus as Magh ("the great"), and 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 
.
.
In MUL.APIN,
Regulus listed as LUGAL, meaning "the star that stands in the breast of
the Lion:the King.".[14]
The entire wiki article on Regulus the star can be found
at: http://en.wikipedia.org/wiki/Regulus
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