Tonight – May 12, 2017 – the waning gibbous moon makes a triangle with the planet Saturn and the star Antares. Watch for this celestial triangle to illuminate your southeast sky by mid-to-late evening. If you’re not one for staying up late, get up before dawn to see the moon, Saturn and Antares lighting up the southwest sky.
Clouded out tonight? The moon will be near Saturn on the night of May 13, too.
Click here for an almanac informing you of the rising times of the moon, Saturn and Antares for your location.
At present, Saturn is traveling in retrograde (westward) in front of the backdrop stars of the zodiac. Saturn’s retrograde started on April 6, 2017 and will end on August 25, 2017. And that means Saturn is now nearly at its best in our night sky. It’s approaching its June 15 opposition – a yearly event for outer worlds like Saturn – as Earth moves around the sun in its smaller, faster orbit. In other words, June 15 is when we’ll pass between the sun and Saturn. That date marks the middle of the best months of 2017 to see this planet.
Because it’s now moving in a westward (retrograde) fashion, Saturn is heading in the direction of Antares, the brightest star in the constellation Scorpius the Scorpion.
Saturn now shines in front of the constellation Sagittarius, but will cross over into the constellation Ophiuchus after a few more days. Saturn will be considerably closer to Antares on the sky’s dome at the end of its retrograde on August 25.
The retrograde motion of the planets baffled the early astronomers. But now we understand it as an event in the course of our orbit, and Saturn’s orbit. Saturn only appears to go backwards (westward) with respect to its normal motion in our sky because Earth travels much more quickly around the sun than Saturn does. We go around the sun nearly 30 times for every one time that Saturn circles the sun.
Therefore, from the moving platform of Earth, Saturn will move in retrograde (backwards) for the next several months as we race toward Saturn – and then away from Saturn. Click here to see Saturn’s retrograde loop for 2017 (and other years).
In the middle of this retrograde on June 15, 2017, Earth will pass between Saturn and the sun, to bring Saturn into opposition from the sun in Earth’s sky (T3, P3 and A3 on the above diagram). At this juncture, Saturn will come closest to Earth for the year, and Saturn, in turn, will shine at its brilliant best in Earth’s sky.
Bottom line: During these next few nights – on May 12 and 13, 2017 – use the moon to find the planet Saturn and the star Antares. Then watch for Saturn to edge closer to Antares on the sky’s dome over the next several months.
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.