The Coachella Valley is a great place for inspiring views of the night sky—and among the visually impressive events is the pairing of Venus and the crescent moon.
While Venus is still visible in the evening sky for a few more months, Venus-Moon pairings will occur at dusk on Sept. 8, Oct. 7 and 8, Nov. 6, Dec. 5, and Jan. 1 and 2. Of these, the pairing this month, on Sunday, Sept. 8, will be the closest, and the moon will even help the observer spot Venus as they move together across the daytime sky.
From Southern California, the moon and Venus appear closest, in the southeast sky shortly after noon, with Venus only 0.6 degrees, or just more than the moon’s width, from the northern cusp or point of the crescent. When the moon and Venus are highest—due south, nearly halfway from horizon to overhead around 3:15 p.m.—they’re more than a degree apart. By sunset, Venus will appear more than 2 degrees to the right of the moon.
As twilight deepens, after 45 minutes, look for Spica within 4 degrees to the lower right of Venus—binoculars will help pick it out of the bright twilight—and Saturn some 11 degrees to the upper left of Venus, and 9 degrees to the upper left of the crescent moon.
But don’t wait until Sunday, Sept. 8, to begin watching! During Labor Day week, the star Spica appears quite close to Venus, only 1.6 degrees to the lower left of the brilliant planet on Thursday evening, Sept. 5. Venus now moves about a degree daily against the background, so it will be easy to notice changes in their arrangement from one night to the next. A thin crescent moon can be easily spotted on Saturday evening, Sept. 7, if you look early enough—say, half an hour after sunset. You may want to keep a log of your sky-watching sessions, with notes and drawings of what you see.
On Sunday evening, Sept. 8, as the moon and Venus sink into the west-southwest—because of the Earth’s rotation—the moon creeps slowly to the upper left of Venus, owing to the moon’s revolution around the Earth. Check again after sunset on Monday evening, Sept. 9, to see how far the moon has progressed in 24 hours. On that evening, Saturn appears about 6 degrees to the right of the crescent moon. By Wednesday evening, Sept. 11, the red supergiant star Antares appears within 7 degrees below the moon, now nearly half-full. On Thursday the 12th, the moon appears just more than half full, having passed first quarter phase, 90 degrees east of the sun, earlier that day. The moon is full overnight Sept. 18-19, rising not long before sunset on the 18th.
For the next several evenings, the waning “Harvest Moon” comes up not much later each night, still rising before 9 p.m. on Sept. 22.
You can follow the waning moon in the morning sky daily an hour before sunrise from Sept. 19 through Oct. 3, watching it pass, in turn, Aldebaran, Betelgeuse, Jupiter, Pollux and Procyon, Mars, and Regulus. (See September’s morning twilight sky map below.)
Daytime Moonwatch: If you have children, take them outdoors daily Sept. 23-Oct. 2 to follow the moon as it changes from 82 percent full on Sept. 23, through 46 percent on Sept. 27 (just after passing last quarter phase, when it’s 90 degrees from the sun), to a thin 6 percent crescent on Oct. 2, just 28 degrees from the sun. The best time for this project is before students go off to school, or even while they are at school (suggest this moon-watch activity to their teacher), in playground time before classes begin, or as late as 9 a.m. This activity can be repeated during Oct. 21 through Nov. 1.
Whenever a planet passes near a star or another planet, the event will be great fun to track nightly for a week before and after the night they’re closest. Evening pairs coming soon include Venus-Spica on Sept. 5, Venus-Saturn 3.5 degrees apart on Sept. 17 and 18, and Venus-Antares 1.5 degrees apart on Oct. 16. Antares is the heart of Scorpius, the Scorpion. Our evening twilight chart for September (above) will help you pick out Venus, Saturn and the brightest stars as they appear about 40 minutes after sunset.
Now in the morning sky, bright Jupiter is a slow-moving planet, taking 12 years to make one circuit around the belt of zodiac constellation. During the 2013-2014 school year, note the changing shape of the triangle Jupiter makes with the Gemini twin stars of Pollux and Castor. During Labor Day week, these twin stars appear 11 to 12 degrees to the lower left of Jupiter, while Mars appears some 20 degrees more steeply lower left of Jupiter. On the weekend of Sept. 7-9, Mars passes through the Beehive Cluster of faint stars, an event best seen with binoculars. In a colorful, pretty pairing on the morning of Oct. 15, reddish Mars will pass within 1.0 degree of the blue-white 1.4-magnitude star Regulus, heart of Leo, the Lion.
Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs. Robert D. Miller did graduate work in Planetarium Science and later astronomy and computer science at Michigan State University, and remains active in research and public outreach in astronomy.