Early skywatchers saw five bright objects slowly moving among the fixed stars. These five were Mercury, Venus, Mars, Jupiter, and Saturn. They called them “planets” from the Greek for “wandering stars.” And to see this wandering for yourself, we focus on three of them this month in the early evening sky.
About 45 minutes after sunset at the beginning of the month, look to the southwest. There, low in the deepening twilight above the horizon is Jupiter. By the 12th it will disappear from view and eventually move into the morning sky next month. To its northeast (upper left) and much higher is brilliant Venus—and to its upper left and higher still is Saturn. Watch each evening as the gap between them narrows to less than just 2 degrees on the 10th and 11th. The ringed planet plays “leapfrog” with Venus, passing each other on the evenings of the 11th to the 13th. By the time Saturn disappears from view into the sunset on the 27th it will have moved 18 degrees to the lower right of Venus. From the upper left of the dazzling planet to the lower right in a matter of just weeks. Wow—no wonder the ancients considered them wandering stars!
While watching these planets go through their antics, you will also be entertained by a beautiful crescent Moon climbing the sky eastward beneath them. On the 28th it will appear as a lovely sliver just 3 degrees under Venus. Binoculars will give the best view of this as well as the other close approaches of the planets themselves.
Incidentally, all planets appear star-like as seen with the unaided eye. But they shine with a steady light as compared to real stars which twinkle as you watch them. The reason is very subtle but quite interesting. Although stars are vastly huge globes (many far larger than our Sun), they are so incredibly far away that their light is reduced to essentially a single “ray.” As such, upon entering the Earth’s atmosphere these rays are easily buffeted around by turbulence and appear to flicker or twinkle to us. The light from planets on the other hand being so much closer to us arrives from their disks in “bundles of rays” rather than single ones and atmospheric turbulence averages out. As a result, they appear to shine with a steady light.
In closing, the annual Geminid meteor shower peaks in the early morning hours of December 14th, but the Moon will only be two days past full and will largely wipe out this wonderful celestial fireworks display. However, if you go outside soon after darkness falls on the early evening of the 13th before moonrise you may be treated to seeing some of the meteors before the sky brightens.
— James Mullaney
Former assistant editor at Sky & Telescope magazine & author of nine books on
stargazing. His latest, Celebrating the Universe!, is available from HayHouse.com.