Antares

Antares A/B

The position of Antares in the Scorpius constellation.
Observation data Epoch J2000      Equinox J2000
Constellation	Scorpius
Right ascension	16h 29m 24s[1]
Declination	-26° 25′ 55″[1]
Apparent magnitude (V)	+1.09[1]
Characteristics
Spectral type	M1.5Iab-b / B2.5V[1]
U−B color index	1.34
B−V color index	1.87
Variable type	LC[2]
Astrometry
Radial velocity (Rv)	−3.4 ±0.9[1] km/s
Proper motion (μ)	RA: −10.16 ±2.03[1] mas/yr Dec.: −23.21 ±1.29[1] mas/yr
Parallax (π)	5.40 ± 1.68[1] mas
Distance	approx. 600 ly (approx. 190 pc)
Absolute magnitude (MV)	−5.28
Details
Mass	15.5 M☉
Radius	800 R☉
Luminosity	65,000(bolometric) L☉
Temperature	3,500 K
Other designations
α Scorpii,[1] 21 Sco,[1] Cor Scorpii, Kalb al Akrab, Scorpion's Heart, Vespertilio, HR 6134,[1] CD -26°11359,[1] HD 148478,[1] SAO 184415,[1] FK5 616,[1] WDS 16294-2626, CCDM J16294-2626A/B,[1] HIP 80763.[1]
Database references
SIMBAD	data

Antares (α Scorpii / Alpha Scorpii) is a red supergiant star in the Milky Way galaxy and the sixteenth brightest star in the nighttime sky (sometimes listed as fifteenth brightest, if the two brighter components of the Capella quadruple star system are counted as one star). Along with Aldebaran, Spica, and Regulus it is one of the four brightest stars near the ecliptic. Antares is a slow variable star with an average magnitude of +1.09.^[1]

Properties

Comparison between the red supergiant Antares and the Sun, shown as the tiny dot toward the upper right. The black circle is the size of the orbit of Mars. Arcturus is also included in the picture for size comparison.

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.^[3] 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)^[4]. This leads to a radius of 822 ± 80 solar radii.

Antares is a type LC "slow irregular variable" star, whose apparent magnitude slowly varies from +0.88 to +1.16.^[2]

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.

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.^[3] 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).^[5] The companion is often described as green, but this is probably a contrast effect.^[3] 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 by Johann Tobias Bürg during one such occultation on April 13, 1819^[6].

The orbit is poorly known, with an estimated period of 878 years.

Position on the ecliptic

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.^[7][8] Every year around December 2 the Sun passes 5° north of Antares.

Antares in ancient cultures

Antares, the proper name of this star, derives from the Ancient Greek Άντάρης, 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. However, it is also thought that Antares may have been named after the ancient Arab warrior-poet Antar. ^[9] Surely, Arab astronomers, by further developing the nautical navigation instrument, the astrolabe, and with their intimate knowledge of the stars and constellations, were also familiar with this star.

Its distinctive coloration has made the star an object of interest to many societies throughout history.

• Many of the old Egyptian temples are oriented so that the light of Antares plays a role in the ceremonies performed there.
• In ancient Persia:

Charles François Dupuis, a French astronomical writer, mentioned that Antares was known as Satevis, one of the four "royal stars" of the Persians around 3000 BC.^[9]

• In ancient India:

It with σ and τ Sco were one of nakshatra (Hindu lunar mansion), as Jyeshthā "Oldest", and Rohinī "Ruddy".^[9]

• 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 .^[10]
• 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).^[11]

Alternative name of this star, meaning "the Heart of Scorpion":

• Calbalakrab from the Arabic Qalb al-Άqrab.^[12] This had been directly translated from the Ancient Greek Καρδία Σκορπίου Kardia Skorpiū.
• Cor Scorpii translated above Greek name into Latin.^[9]

See also

• Antares in fiction

References

External links

• A comparison of the size of Antares to other celestial objects
• Exploring the Full Stellar Population of the upper Scorpius OB Association
• Antares on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Coordinates: 16^h 29^m 24^s, −26° 25′ 55″