The Red Supergiant Star Antares

Antares, α (alpha) Scorpii, is a red variable star and the brightest star in the constellation of Scorpius (the Scorpion), located at an estimated distance of 550 light-years. The sixteenth brightest star in the night sky, Antares is one of the best-known supergiants, which are extremely massive and intrinsically brilliant stars. Though it rates as quite cool by stellar thermometer standards, with a surface temperature of only about 3300 degrees Celsius, Antares’ visual luminosity exceeds the Sun’s by over 10 000 times.

Antares dwarfs the Sun in size as well. Approximately 800 times bigger in diameter than our neighbourhood star, Antares’ outer surface would stretch beyond the orbit of Mars if it took the Sun’s place. Despite its girth, Antares has a mass of only 15 to 18 solar masses, giving this colossal star a very low average density.

Antares is also a binary system, with a hot blue companion called Antares B. A rare yellow and orange-coloured reflection nebula enshrouds both stars.

Each year around 31 March, Antares is at opposition to the Sun and hence best seen from Earth. As the year reaches its end, around 30 November, Antares is outshined by the Sun’s glare, making it impossible to see for almost three weeks.

Due to its reddish complexion that is similar to that of Mars, Antares’ name derives from a Greek Αντάρης (Ant-Ares) which means "against Mars".