This evening, as soon as darkness falls, look for the beautiful grouping of the thin waxing crescent moon and the red planet Mars, joined by the red star Antares. The threesome appears low on the southwest horizon. Antares, the brightest star in the constellation Scorpius, and Mars, the fourth planet from the sun, shine at nearly the same brightness, although Antares is technically the brighter of the two. Be sure to catch all three – the waxing crescent moon, Mara and Antares – at dusk and early evening, because they’ll follow the sun beneath the southwestern horizon shortly after nightfall.
Mars and Antares should be easy to pick out of the sky as they will be the brightest objects near the moon. Both are a reddish color. In Greek, Antares means “rival of Mars.” Scorpius is one of 13 constellations on the ecliptic—the path we observe from Earth that the sun, moon and planets follow across the sky. Every couple of years Mars, on its orbit around the sun, moves near its “rival” star, Antares, in the constellation Scorpius.
Mars gets its red color from oxidized (or rusted) iron-rich materials on its surface and in the atmosphere. Antares is red because of its temperature. From Earth we can guess a star’s temperature based on its color, much like a campfire—the whiter the flame, the hotter the color. Antares is a red supergiant and is relatively cool at 3500 Kelvins (about 5800 degrees F, compared to our sun’s 10,000 degrees F). Supergiants are huge and bright. If Antares were in our sun’s place it would swell out to somewhere between Mars and Jupiter.
Step outside this evening, after the sun has set, and look to the west and find the waxing crescent moon, Mars and its rival red star Antares.