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Antares is a class M supergiant star, with a radius of
approximately 800 times that of the sun; if it were placed in the
center of our solar system, its outer surface would lie between the
orbits of Mars and Jupiter. Antares is approximately 600 light-years
(180 pc) from our solar system. Its visual luminosity is about
10,000 times that of the Sun, but because the star radiates a
considerable part of its energy in the infrared part of the
spectrum, the bolometric luminosity equals roughly 65,000 times that
of the Sun. The mass of the star is calculated to be 15 to 18 solar
masses.[2] Its large size and relatively small mass give Antares a
very low average density.
The size of Antares may be calculated using its parallax and angular
diameter. The parallax angle is given in the Starbox to the right,
and the angular diameter is known from lunar occultation
measurements (41.3 ± 0.1 mas)[3]. This leads to a radius of 822 ± 80
solar radii.
The best time to view Antares is on or around May 31 of each year,
when the star is at opposition to the Sun. At this time, Antares
rises at dusk and sets at dawn, and is thus in view all night. For
approximately two to three weeks on either side of November 30,
Antares is not visible at all, being lost in the Sun's glare; this
period of invisibility is longer in the Northern Hemisphere than in
the Southern Hemisphere, since the star's declination is
significantly south of the celestial equator.
[edit] Companion star
Antares has a hot blue companion star, Antares B, of spectral type
B2.5 at a separation of about 2.9 arcseconds, or 550 AUs at Antares'
estimated distance.[2] At magnitude 5.5, it is only 1/370th as
bright visually as Antares A, although it shines with 170 times the
Sun's luminosity. It is normally difficult to see in small
telescopes due to Antares' glare, but becomes easy in apertures over
150 mm (5.9 in).[4] The companion is often described as green, but
this is probably a contrast effect.[2] Antares B can be observed
with a small telescope for a few seconds during lunar occultations
while Antares itself is hidden by the Moon; it was discovered during
one such occultation on April 13, 1819.
The orbit is poorly known, with an estimated period of 878 years.
[edit] Position on the ecliptic
Antares near the Sun, event which occurs on December 2 every year.
Image from SOHO.Antares is one of the 4 first magnitude stars that
lies within 5° of the ecliptic and therefore can be occulted by the
Moon and rarely by the planets. On 31 July 2009, Antares was
occulted by the moon. The event was visible in much of southern Asia
and the Middle East.[5][6] On 17 November 2400 Antares will be
occulted by Venus[citation needed]. Every year around December 2 the
Sun passes 5° north of Antares.
Of the 21 first-magnitude stars, Antares now lies farthest in
angular distance from any other first-magnitude star; i.e. it is
possible to draw a larger circle centered around Antares without
including any other first-magnitude star inside that circle, than
around any other first-magnitude star. The nearest first-magnitude
star to Antares is Alpha Centauri, lying approximately 39°6.75′
away. The high proper motion of Alpha Centauri is gradually
increasing this angle. Before about March 2000, Achernar and
Fomalhaut held this distinction of being the most isolated from
other first-magnitude stars.[citation needed]
[edit] Antares in ancient cultures
Antares' name derives from the Ancient Greek Αντάρης, meaning
"(holds) against Ares (Mars)", due to the similarity of its reddish
hue to the appearance of the planet Mars. It is the brightest star
in the constellation Scorpius. Its distinctive coloration has made
the star an object of interest to many societies throughout history.
According to ancient Arab tradition, Antares is the warrior-poet
Antar's star[citation needed]. Many of the old Egyptian temples are
oriented so that the light of Antares plays a role in the ceremonies
performed there. Antares was also known as Satevis in ancient Persia
and was one of the four "royal stars" of the Persians around 3000
BC[citation needed]. It was also known as Jyeshtha in ancient India.
In the religion of Stregheria, Antares is a fallen angel and quarter
guardian of the western gate. In astrology, Antares is one of the
Behenian fixed stars and has the symbol .[7]
An old Arabic name was Ķalb al Άķrab, the 'Scorpion's heart.' This
had been directly translated from the Ancient Greek Καρδια Σκορπιου
Kardia Scorpiou and Latin Cor Scorpii.[7]
The Wotjobaluk Koori people of Victoria knew Antares as Djuit, son
of Marpean-kurrk (Arcturus); the stars on each side represented his
wives. The Kulin Kooris saw Antares (Balayang) as the brother of
Bunjil (Altair).[8]
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