MANITOBA SKIES – December 2017
December brings our calendar to a close, and contains several interesting events (and a few non-events) for skywatchers. With the sun setting so early, you can get in a few hours of stargazing without staying up too late.
December's "supermoon": According to some, the full moon on December 3 will be a “super moon”. What exactly does that mean? The Moon will be near its closest point to earth at the time of full moon, something that happens two or three times a year. This means the moon will appear several percent larger than other full moons. Here’s the thing: in this case, the word “super” builds up false expectations. Several percent is not enough to really notice unless you have something to compare it to – but of course, you can’t compare it to previous full moons except by memory, and that is not reliable enough. I’ve seen a lot of reports that the moon looks “extra big and bright” but I suspect that is mostly a case of expectation and not observation. Unless you’re a very careful observer, you just won’t notice the difference. Gary Seronik of SkyNews Magazine explains more here.
Still, the December full moon is a great thing to observe. The geometry of the solar system means that the moon will be in the constellation of Gemini, amongst the bright winter stars, and will shine high overhead at midnight. The glow of moonlight on the snow makes the night seem very bright, a welcome sight at the darkest time of the year.
Winter Solstice: Speaking of the time of year, December contains an important date on the celestial calendar. The Winter Solstice (as it’s called in the northern hemisphere) marks the sun’s lowest point in our sky. The sun sets farthest south of west, and rises the farthest south of east, of the entire year. It only rises partway up the sky before sinking back, and we have long nights compared to daylight hours. In 2017, the solstice occurs at 10:28 a.m. Central Standard Time on December 21st, and this marks the beginning of winter in the northern hemisphere. The reasons for the seasons can be found in the tilt of the earth’s axis as it goes around the sun, as described here. The planetarium’s December show, Season of Light, has a great scene where this is described in detail. The show also goes into the various celebrations around the world that occur at this time of year.
Geminid meteor shower peak: In the early morning hours of December 14th, the Geminid meteor shower will provide a decent show. The moon will be out of the way, and so if you can avoid city lights as well, you may see a meteor every minute or so. The Geminids are arguably the best meteor shower of the year, even beating out the more-comfortable-to-observe Perseids of August. Further details on observing the Geminids can be found here.
Both Saturn and Mercury lie too close to the Sun in the evening sky to be visible at the start of the month. Mercury just peaks above the horizon near the end of the month, gearing up for its January appearance.
In the hour before sunrise, three bright planets come up above the eastern horizon. Mars rises in the east about 4 a.m., slightly above the star Spica in Virgo, getting brighter and moving higher over the course of the month. Mars' ruddy hue contrasts well with the blue-white glow of Spica. Jupiter pops up next, chasing Mars across the sky. Venus is lost in the sun's glare very early in the month, but you might catch it just before sunrise on the first few mornings of December.
To see where things are in the night sky, visit Heavens-Above's excellent Sky Chart page for Winnipeg, and adjust the times and dates for when you will be observing. For other locations, visit the Settings page and choose the nearest city or town.
Sky Events - December 2017
All times below are given in Central Standard Time (CST), the local time zone for all of Manitoba.
3 Dec 2017: Full Moon.
10 Dec 2017: Last Quarter Moon.
12 Dec 2017 (morning): The waning crescent moon, the bright star Spica, and the planet Mars form an inverted triangle in the early morning sky.
13 Dec 2017 (morning): The moon has moved to hover over Mars in the morning sky.
13-14 Dec 2017 (all night): The Geminid meteor shower peaks tonight and tomorrow morning. Rates are likely to increase after midnight, but this is one of the few meteor showers where the evening rates can be decent as well.
14 Dec 2017 (morning): The thin crescent moon has leapfrogged Mars and now sits overtop of Jupiter in the morning sky.
18 Dec 2017: New Moon.
26 Dec 2017: First Quarter Moon. Also on this date, you might be able to begin to glimpse Mercury as it peaks above the eastern horizon just before sunrise, but you'll need a very clear sky, a horizon clear of any obstructions, and probably a pair of binoculars.
To spot the International Space Station as it passes over southern Manitoba, visit Heavens-Above.com which calculates times and directions for you.