Alpha Scorpii


Distance (Light Years) 600 ± 190
Apparent Magnitude 1.06
Color (B-V)1.83

Names For This Star

The name Antares derives from Greek: anti ares meaning "The Rival of Mars." The name may have to do with the color of the star or with its placement in the constellation of Scorpius, which was particularly associated with Mars in astrology.

Other names for the star are the Latin Cor Scorpii, "The Heart of the Scorpion.". The Arabic Kalb al Akrab means the same thing.

The The Bright Star Catalog offers Vespertilio as yet another name for the star. According to Allen this name means a "Bat" and may go back to the Athenian tragedian Sophocles.

Description of the Star

Antares A is the cool red M1.5Iab-Ib supergiant primary of a double star system. The effective temperature is about 3100 K. The star is approximately 10,000 times as luminous as the sun. Acccording to Burnham Antares A would have a mass of 10 to 15 times that of the sun.

This huge star has a radius that is probably almost 4 AU. If the sun were replaced by Antares A at the center of the solar system, the earth would be engulfed, as would be Mars and the Asteroid Belt. Jupiter would orbit about 1 AU from the surface of the star!

The companion star is a hot blue B4Ve main sequence star. The spectral type implies an effective temperature of 18,000 K.

The companion Antares B is itself larger than the sun, with a diameter about 4 times that of the sun and a mass almost 10 times that of the sun. This star would be about 1900 times as luminous as the sun.

According to the The Bright Star Catalog the orbital period of the two stars about their common center of mass is 878 years. The semimajor axis of the orbit is 2.90 sec of arc corresponding to 540 AU at the distance of the stars. This is about 14 times the radius of the solar system out to Pluto.

Study of the dynamics of the orbit implies a mass of 15.5 times the sun for Antares A and a mass of 7.0 times the sun for B.

Other Designations For This Star


21 Scorpii

Hipparcos Identifier (HIP Number)


Harvard Revised (HR Number)


Henry Draper Catalog (HD Number)


Bonner Durchmusterung (BD Number)

Smithsonian Astrophysical
Observatory compendium (SAO Number)

Fundamental Katalog (FK5 Number)



Copyright © 1998 - 2010 by Arnold V. Lesikar,
Professor Emeritus
Dept. of Physics, Astronomy, and Engineering Science,
St. Cloud State University,St. Cloud, MN 56301-4498

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