Fred Barrett | Dec 12, 2018
This should be a great month for comet lovers. Comet 46P Wirtanen will be a naked eye sight in the sky. It’s small, just barely 1 Km in diameter, but its orbit will pass very close to Earth making it appear like a much bigger object. It’s already in the night sky but still at a distance where binoculars are necessary to view it. The gases that it is venting make it appear as large as the moon but its small size limits the amount of gases and dust it puts out and this low density keeps its brightness low. Thus you will need a small telescope or a pair of 7x50 binoculars for best views. Its closest approach will be on December 16th when it will be just 11.5 million km away – that’s only 30 times farther than the Moon. At this distance, it should easily be seen with eyes only despite its low brightness. Remember though that comets are surprisingly unpredictable and maybe an extra burp of gas and dust will give it an extra boost in brightness. It will be one of the 10 closest comets to pass Earth in recent times. It won’t be a great comet but certainly will be a fantastic sight. Between the 13th and 17th it will be easily found between the bright red star Aldebaran, the eye of the Bull in the constellation Taurus, and the Pleiades. Refer to the attached sketch for the path of its orbit.
This month we also have another treat! The Geminids make their annual appearance and are a truly spectacular shower that is viewable from December 4th to about the 17th. The peak is on the night of the 14th.There may be as many as 120 meteors per hour with the added bonus that there is a waxing non interfering crescent Moon which sets at 11pm leaving the sky free and clear. The radiant is high in the south just above Castor in the constellation Gemini. It’s best not to view them by looking at the radiant since the meteors are coming at you head on. This means that their trails will be very short. Instead, look about 30 to 60 degrees away from the radiant for nice long trails.
Venus is a dazzling sight in dawn sky to the southeast. Down and to the left you will find Mercury and Jupiter. By the 21st, Jupiter will rise up to within 1 degree of Mercury. In the evening sky, Mars is quite obvious in the constellation Aquarius in the south. Saturn is very low in the southwest.
December 12th: The Moon is at apogee – 402,800 km. December 14th: The annual Geminid meteor shower peaks. The Moon passes 4 degrees south of Mars at 6pm. December 15th: First quarter Moon. December 21st: Winter solstice – 5:23 pm EST. Yahoo, the days start getting longer but don’t throw your long johns out yet! December 22nd: Full Moon. This Moon is known as the Full Cold Moon or the Full Long Nights Moon. In December the nights are cold and long. I spend my days hauling wood to my fireplace and I’m pretty muscle bound by the end of March! December 24th: The Moon is at perigee – 358,960 km. December 29th: Last quarter Moon. December 24th: The Moon is at perigee – farthest. 358,960 Km. December 29: Last Quarter Moon. That’s a wrap. Keep looking up!
“The Beginner’s Observing Guide by Leo Enright is an invaluable companion for adventures in the sky. It also contains useful star charts. It can be ordered from the Royal Astronomical Society of Canada at www.rasc.ca/publications. A subscription to our very own excellent Canadian astronomy magazine “SkyNews” can be arranged at the RASC website as well.