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Antares (α Sco / α Scorpii / Alpha Scorpii) is the brightest star in the constellation Scorpius and one of the brightest stars in the nighttime sky. Along with Aldebaran it is one of the two brightest stars in the zodiac, and their constellations Scorpius and Taurus also lie directly opposite one another.

Antares' name derives from the Greek ανταρης, meaning "(holds) against Ares (Mars)", due to the similarity of its reddish hue to the appearance of the planet Mars. This distinctive coloration has made the star an object of interest to many societies througout history, and many of the old Egyptian temples are oriented so that the light of Antares plays a role in the ceremonies performed there. Antares was one of the four "royal stars" of the Persians around 3000 BC, and some writers claim that it is the "lance star" referred to in the Biblical book of Job. In the religion of Stregheria, Antares is a fallen angel and quarter guardian of the western gate .

Antares is a class M giant star, with a diameter of approximately 9.24 × 108 km, or slightly more than the distance as from Sun to Mars, and is approximately 520 light years from earth. It has a very low density.

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 a few degrees south of the ecliptic.

Antares has a hot blue companion star (Antares B) at a distance of about 2.7″. Although it is 5th magnitude, it is normally difficult to see because of Antares' glare, but can be observed with the naked eye 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 orbital period is 878 years.

In 1971, NASA chose to name the Apollo 14 lunar module after the star.

Last updated: 08-17-2005 21:08:02