This Week’s Sky: December 11 – 18

The Geminid meteor shower peaks in moonless skies.

Doug Nan Jiang captured this superb image of the Double Cluster in Perseus—one of the season’s finest deep-sky objects for small telescopes and binoculars.

All Week

The view facing southeast at 6 a.m. local time, midweek.

Planet watchers will have to rise early for the time being. With Saturn now too close to the Sun to be observed, the evening sky is devoid of bright planets. But if you venture outdoors around 6 a.m., local time, you’ll be greeted by Jupiter and Mars reasonably high in the southeast. At magnitude –1.7, Jupiter is the most conspicuous dot of light in this part of the sky and is impossible to miss. But Mars isn’t doing too badly, either. The red planet shines at magnitude 1.6, which makes it only ½-magnitude fainter than nearby Spica. Jupiter is gaining altitude and gradually becoming a more interesting telescopic sight. Indeed, even now, you might get the occasional satisfying view of Jupiter when the atmosphere is steady. Mars, on the other hand, is still very tiny and won’t be worth inspecting in a scope for several more months. Finally, you might catch a glimpse of magnitude –3.9 Venus in bright twilight. After nine months as the morning “star,” Venus’s reign is coming to an end, for it now rises only half an hour before the Sun.

December 13

The view facing southeast at 5:30 a.m., local time.

This morning the waning crescent Moon sits a little less than five degrees from Mars. Both objects are positioned roughly nine degrees from first-magnitude Spica, for an attractive predawn gathering that also includes Jupiter.

December 13/14

Chart by Glenn LeDrew

The Geminid meteor shower peaks tonight. This is one of the best annual meteor displays, though it’s often hampered by the season’s frequently cloudy and chilly weather. But this year, the shower’s other nemesis—moonlight—isn’t a factor. Although you can begin your Geminid watch on the evening of the 13th, the best time to view will be around 1 a.m., local time. That’s when the shower’s radiant is nearly overhead and well before the crescent Moon rises. How many Geminids will you see? Under ideal dark-sky conditions you might catch as many as 120 per hour, but light pollution will diminish that rate significantly. Regardless, if your sky is clear, be sure to bundle up and enjoy the show. (For more on the 2017 Geminids, turn to page 29 of the November/December issue of SkyNews.)

December 14

Jupiter and the Moon as seen in 10×50 binoculars.

This morning it’s Jupiter that gets a visit from the Moon. The lunar crescent has travelled eastward and is now some four degrees above Big Jove. That means both objects will fit into the same binocular field, though the sight can be enjoyed equally well without optics.

December 18

New Moon occurs at 1:18 a.m., EST, this morning.

Weekend Stargazer

Use this chart to locate the Double Cluster in Perseus. (Click on the image for a full-size version.)

Evenings over the December 15 – 17 weekend are free from moonlight, with new Moon occurring Sunday night/Monday morning. For deep-sky observers willing to bundle up, a sparklingly clear night will be irresistible. And with darkness falling so early, you can get in a lot of sky time before bedtime. That’s the offsetting benefit to the season’s cold temperatures. So what is there to see? How about the famed Double Cluster in Perseus.

In spite of their prominence, these side-by-side clusters didn’t make into Charles Messier’s well-known list of non-comets. The eastern and western clumps of stars are catalogued, respectively, as NGC884 and NGC869. To really appreciate the Double Cluster, you have to be able to see both halves at the same time. That means using an instrument capable of providing a field of view around two degrees across. Less than that and the glittering duo begins to lose some of its splendour. This is one example of small telescopes having the advantage over big-aperture light buckets. Even binoculars provide a wonderful view of the Double Cluster and its surroundings.

After soaking in the wide-field perspective, try inspecting the component clusters individually with your telescope at moderate magnification. Each grouping is rewarding in its own right and it’s fun to compare them. Which one appeals to you more? And don’t forget to note the striking sprinkle of orange stars scattered among the ice-blue cluster gems. Sights like these make the cold weather just a bit easier to take.

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