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This Week’s Sky: December 10 – 17

Comet 46P/Wirtanen is at its best and Geminid meteors streak.

Comet photographed by Alan Dyer

SkyNews contributing editor Alan Dyer captured this view of Comet 46P/Wirtanen on December 6. To see more of Alan’s images, visit his web site, AmazingSky.com.

All Week

Facing southeast, 45-minutes before sunrise.

The view facing southeast, 45-minutes before sunrise.

Although it won’t be easy, it’s possible to see all five naked-eye planets this week—two at dusk, and three at dawn. The dusk twosome are Mars and Saturn. Glowing at magnitude 0.2, Mars is an easy catch as it transits the meridian at roughly 6 p.m., local time. Saturn, however, sits low in the southwest during twilight. You’ll need binoculars and an unobstructed view to catch the magnitude 0.5 ringed planet as it hovers just 4 degrees above the horizon 45 minutes after sunset. The dawn planetary trio is quite a bit easier. In the “can’t miss it” category is Venus, gleaming like a beacon at magnitude –4.8. The morning “star” rises at 4 a.m. and is well up before the first hint of twilight. Trailing behind are the two horizon huggers, Mercury and Jupiter. Mercury shines at magnitude –0.4 and is in the midst of its most favourable apparition for 2018. The little planet reaches an altitude of nearly 10 degrees, 45 minutes before sunrise. At that same time, Jupiter sits just 3 degrees above the southeast horizon. The magnitude –1.7 gas giant is re-emerging from its November 26 conjunction with the Sun, and climbs slightly higher each morning.

December 13/14

Geminid chart

The Geminid meteor shower radiates from a region of sky near the stars Castor and Pollux. This is the view facing east at roughly 9:30 p.m. local time on December 13. (SkyNews chart by Glenn LeDrew)

The Geminid meteor shower reaches its peak tonight. This is one of the year’s two finest displays (the other being the August Perseids) and, if you have clear skies, it’s one you don’t want to miss. Conditions this year are nearly ideal, with the crescent Moon setting as the shower’s radiant climbs high in the northeast. The best time to look for Geminids is in the predawn hours of December 14. That’s when the radiant point is high overhead and the display is expected to be reaching its peak. How many meteors will you see? That depends a great deal on local conditions. In a dark country sky free from light pollution, up to 80 Geminids per hour isn’t out of the question. Just remember to bundle up and have a hot beverage on hand. (For detailed information on the display, turn to page 28 of the November/December issue of SkyNews.)

December 14

Facing West at 9 p.m., local time.

The view facing West at 9 p.m., local time.

This evening the waxing crescent Moon and Mars are positioned less than five degrees apart. The pairing will be a fine naked-eye sight and a delight in binoculars. The two objects will be closest around 11:15 p.m., EST (8:15 p.m., PST), which favours observers on the West Coast, where the duo will be higher.

December 15

The Moon is at first-quarter phase at 6:49 a.m., EST.

Mercury reaches greatest elongation in the morning sky today and is well positioned for viewing at dawn.

December 16

This evening Comet 46P/Wirtanen is positioned near the Pleiades in what will likely be the highlight of the comet’s current apparition. Coincidentally, it’s also closest to Earth. (See Weekend Stargazer, below for details).

Weekend Stargazer

Comet 46P/Wirtanen chart for December 10 to 16

Use this chart to locate Comet 46P/Wirtanen this week. (Click on the image for a full-res version.)

The December 14 – 16 weekend is prime time for Comet 46P/Wirtanen. In addition to its lovely flypast of the Pleiades cluster this weekend, the comet drifts closest to Earth, lying only 11.5 million kilometres from us on December 16. That’s 30 times farther away than the Moon, but good enough to make Wirtanen the 10th closest cometary encounter we’ve had since 1950. For many long-time sky watchers, 46P/Wirtanen brings back memories of another close encounter—1983’s Comet IRAS-Araki-Alcock. Like the great comet of ’83, Wirtanen appears in the sky as a large, diffuse puffball.

The most recent reports indicate that Comet 46P/Wirtanen is glowing at magnitude 5 and can be glimpsed with the naked eye (or more easily in binoculars) under a dark country sky. By the weekend, the comet should be even brighter. However, its diffuse nature means it’s likely to suffer from light pollution more than similarly bright comets. Under adverse sky conditions Wirtanen may not stand out as well as its magnitude number suggests. Regardless, this is the finest comet we’ve had in some time, so it’s worth braving the cold and making an effort to get to a good local observing site to take in the show.

For more on Comet 46P/Wirtanen, turn to page 29 of the November/December issue of SkyNews.

At SkyNews we love to read about your experiences and see your photos. You can share them with us by e-mailing [email protected].

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