Around the Sky in 28 Days – Day 5

Tonight the Moon visits the bright star Antares, the “heart” of Scorpius. This obviously red star is the 15th brightest in the sky at an average magnitude of +1.0. We say “average magnitude” because like many red supergiants Antares is a variable star and can brighten and dim by a few 10s of percent. It is truly a supergiant star. If it were located in our solar system it would extend past the orbits of Mercury, Venus, Earth and Mars to a point well within the asteroid belt. That’s over 800 solar radii. Located a distance of 550 lightyears, Antares produces up to 60,000 times as much energy as the Sun though due to its relatively cool surface most of this energy is radiated in the infrared. It is massive enough at 15-18 solar masses that it will end its life as a brilliant supernova.

The name Antares is Greek and means “like Ares (Mars)” or “holds against Ares (Mars)”. The Greek Ares was the equivalent of the Roman Mars. Both the planet and the star are similar in color and often similar in brightness. Try comparing Antares with slightly fainter Mars which is still located low in the southwest just below bright Venus.

Tomorrow – Day 6 – The Moon passes the heart of the Milky Way.