For better or worse, the year 2017 finally comes down to its last month. Our planet, to be sure, has had better years. But the heavens, as always, offer respite.
This month has many beautiful sights and events for attentive sky watchers. The Moon acts as your guide in December to the planets and bright stars along the ecliptic, especially the brightening planets Mars and Jupiter in the pre-dawn sky. Saturn finally disappears westward into the Sun for the year after a fine apparition in 2017, while Venus disappears eastward into the Sun’s glare by mid-month. There are two fine meteors showers in December. And the seasons change once again as winter begins in the northern hemisphere and summer begins in the south. Here’s what to see in the sky this month…
3 December. Full Moon, 15:47 UT
3 Dec. The Moon is at perigee tonight, its closest approach to Earth during the month. This is the last Full Moon of 2017. Look for the bright star Aldebaran just one or two finger widths away, depending on your location.
9 Dec. The waning gibbous Moon lies three finger widths to the east of the bright star Regulus in the constellation Leo. It’s an inspiring sight for early risers on a cold northern morning, or a warm late-spring morning for observers in the southern hemisphere.
10 Dec. Last Quarter Moon, 7:51 UT
13 Dec. As it makes its way eastward along the ecliptic, the thin crescent Moon lies just 5º to the north of the planet Mars in the eastern and southeastern sky before dawn. The Red Planet has been on the other side of the Sun for much of the past year, but the Earth is slowly catching up to it on the way to a splendid Martian opposition in the summer of 2018. Get your telescope ready!
13-14 Dec. Look for the Geminid meteor shower in the late hours of December 13 and in to the morning of the 14th. One of the best and most reliable meteor showers, the Geminids are favored this year by a waning crescent Moon which keeps the sky relatively dark. You can see Geminids anywhere in the sky and from anywhere on Earth. They trace their path back to a point in the constellation Gemini near the star Castor. If possible, look just after dark for a few Geminids as they enter the atmosphere at a shallow angle and burn slowly across the sky. The meteor shower happens on this date each year as the Earth passes through a stream of debris from the asteroid 3200 Phaethon, a somewhat mysterious asteroid discovered only 35 years ago.
14 Dec. A wafer-thin crescent Moon has moved eastward again to tangle with the bright and brightening planet Jupiter in the eastern sky before sunrise. Jupiter slowly brightens and grows larger during the month. If you’re up early with your telescope, have a look at the big planet! It moves closer to Mars as December progresses. The two will make a close approach to each other early in 2018.
18 Dec. New Moon, 6:30 UT
21 Dec. The Sun reaches its most southerly point on the ecliptic at the Winter Solstice. This marks the beginning of winter in the northern hemisphere and summer in the southern hemisphere.
21-22 Dec. December’s other meteor shower, the Ursids, peaks tonight and tomorrow morning. The meteors appear to originate from a point near the star Kochab in the constellation Ursa Major in the far-northern sky. This shower features about 10 meteors per hour, with possibly more, while the Moon stays mostly out of the way as it waxes in the western sky after sunset. This somewhat obscure meteor shower occurs as the Earth passes through the debris stream of the periodic comet 8P/Tuttle. Given the far-northern location of the radiant, the Ursids favors northern observers.
25 Dec. It is Christmas Day! If you’ve got time on your hands, as you wait for Christmas dinner to coalesce, have a look at this fascinating article about how to cook a turkey… on Venus!
26 Dec. First Quarter Moon, 9:20 UT
30 Dec. The gibbous Moon appears very close to the bright star Aldebaran. The Moon passes in front of the star for many observers in North America and Europe. You can look up the timing of the occultation at this link.
31 Dec. Look for Jupiter and Mars on either side of the 3rd-magnitude star Zubenelgenubi (α Librae) in the eastern pre-dawn sky.
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