This article is about the star. For other meanings, see Antares (disambiguation)

Antares (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, Spica, and Regulus it is one of the four brightest stars near the ecliptic. The similarly colored Aldebaran lies almost directly opposite Antares in the Zodiac.

Antares in ancient cultures

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Properties

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Antares is a class M supergiant star, with a diameter of approximately 1.33 × 10⁹ km, or if in place of our sun, it would slightly more than encompass the average orbit of Jupiter, and is approximately 600 light years from earth. Visually, its luminosity is about 10,000 times that of the Sun but overall, taking into account that the star radiates a considerable part of its energy in the infrared part of the spectrum the luminosity equals roughly 65,000 times that of the Sun. The mass of the star is calculated to be 15 to 18 solar masses. Its large size and relatively small mass give Antares 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.

Companion Star

Antares has a hot blue companion star (Antares B) at a distance of about 2.9″. 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.

Position on the Ecliptic

Of the 21 first-magnitude stars, Antares now lies further in angular distance from any first-magnitude star than any other first magnitude star, i.e. you could draw the largest circle centered around Antares without including any other first-magnitude star inside that circle. 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.

In 1971, the crew of Apollo 14 named their lunar module after the star.

Bayer objects | Binary stars | Blue-white dwarfs | Red giants | Red supergiants | Scorpius constellation

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