Tonight (June 11) the moon returns to the constellation Scorpius the Scorpion, shining below the planet Saturn at nightfall. The brightest star in the moon’s vicinity vicinity is Antares, whose name means “like Mars,” because of its similar ruddy hue to the red planet. If you remember your Greek mythology, or perhaps episodes of Xena: Warrior Princess, Ares is the god of war, the counterpart to the Roman god Mars. You can perform the color comparison yourself, because the planet Mars lies in the southwest sky, somewhat close to Spica, the brightest star in the constellation Virgo the Maiden.
We expand the above chart to include much more sky in the sky chart below, to highlight the star Spica and the planet Mars. Throughout June 2014, the planets Mars and Saturn plus two bright zodiacal stars, Spica and Antares, will enable you to view the ecliptic – the Earth’s orbital plane projected onto the dome of sky – with the mind’s-eye.
Some people ask why is Antares so red? Because the outer layer of its atmosphere – its “surface” for lack of a better term for a giant ball of gas – is cooler than other stars that appear whitish. It’s still very hot by earthly standards, some 3,100 degrees Celsius (5,600 degrees Fahrenheit), but a far cry from our sun’s surface temperature of 5,200 degrees C (9,400 degrees F). As a result, the light we see from Antares comes mostly from the red side of the spectrum.
And here’s another bit of word origins: the moon’s almost-full phase tonight is called “gibbous,” which derives from the Latin word for “hump.” Do you have binoculars? If so, they may help you to better discern the reddish color of Antares and Mars on this moonlit night.