Tonight – May 11, 2017 – and for the next few evenings, watch for the waning gibbous moon, the star Antares and the planet Saturn to rise above your southeast horizon by mid-to-late evening. If they’re not up before your bedtime, you can look for this celestial threesome – the moon, Antares and Saturn – in the western half of the sky before morning dawn.
Click here for recommended almanacs; they can help you find the rising times of the moon, Antares and Saturn into your sky.
Saturn is nearly at its best and will be closer to the moon on the night of May 12. Read more about Saturn at tomorrow’s night sky post.
Or check out this article on Saturn: Got 5 minutes? Learn to see Saturn
Tonight, focus on ruddy Antares, the brightest star in the constellation Scorpius the Scorpion. It’s a red supergiant star, whose immense size makes our sun appear puny. Although Antares’s size isn’t known with absolute precision, it’s thought that its radius is better than three times the Earth’s distance from the sun, a distance commonly called the Astronomical Unit (AU).
In other words, if Antares replaced the sun in our solar system, its circumference would extend well beyond the orbit of Mars and roughly 60% the way to Jupiter. Yes, our sun is huge, with the diameter of 109 Earths and the volume of about 1.3 million Earths. Yet Antares’ diameter spans about 650 sun diameters and its volume is somewhere around 275 million suns. Talk about gargantuan!
The name Antares means “like Mars” because of the similarity in color (and sometimes brightness) of Antares and the red planet Mars. In February 2018, Mars and Antares will be in conjunction and at virtually the same brightness, giving you an opportunity to try to distinguish the ruddy star from the red planet in the morning sky.
Bottom line: On the nights of May 11, 12 and 13, 2017, watch for the bright waning gibbous moon to shine near the red star Antares and golden planet Saturn.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.