Once again, the year has rolled around or, at least, will roll around to that time when we witness the shortest day and the longest night.
The astronomical term for this event is the winter solstice, when the sun's daily maximum elevation in the sky is at its lowest, resulting in less daylight and, consequently, a longer night.
The winter solstice usually occurs on Dec. 21 or Dec. 22. For us here in the northern hemisphere, it signifies the official beginning of the winter season and, in the southern hemisphere, the beginning of the summer season.
Winter officially begins for us here in Atlantic Canada on Dec. 22 at approximately 1:30 a.m. AST. Our northern hemisphere is tilted at its maximum angle away from the sun in December, with the resulting decrease in the amount of direct sunlight we receive and the ensuing colder weather. The ironic thing about this is that the Earth is actually closer to the sun in December than it is at the time of the summer solstice in June. Many ancient cultures around the world celebrated this astronomical event and its resulting change in seasons with festivals. Our Christmas celebration has ties to this ancient custom. For more information of solstices, check the Internet.
A number of bright planets populate December's evening and pre-dawn sky. Mercury, which we last glimpsed in November low in the western evening sky, disappears behind the sun for the greater part of the month and doesn't make an appearance until the latter part of December in the eastern, pre-dawn sky. Look for Mercury in the east just before dawn on Dec. 22, when it will be at its highest point in the sky. It will be joined by the waning crescent moon to the lower right.
As it was in the process of doing when November closed, Venus continues to climb high in the south-west, evening sky, appearing as the first evening star. On the evening of Dec. 26, Venus is joined by the waxing, crescent moon to its right. Mars, brightening slightly as the month progresses, can be found in the south-west, pre-dawn sky. On Dec. 17, the last quarter moon sits just below Mars.
Jupiter shines majestically high in the southeast sky as darkness falls. The gibbous moon sits near Jupiter on the evening of Dec. 6. Saturn is the morning star throughout December, sitting high in the southern sky near the star, Spica, in the constellation of Virgo - the Maiden in the pre-dawn hours. On Dec. 20th, the waning, crescent moon passes below Saturn and Spica.
As fortune dictates, viewing of December's Gemind meteor shower (peak on the night of Dec. 14) will be dramatically reduced due to the gibbous moon. However, as the moon does not rise until around 9 p.m. that night, there is about a two-hour window of opportunity between sunset and moonrise to catch a view of this fairly reliable meteor shower. Its radiant is in the constellation of Gemini - the Twins, which rises in the east as darkness falls.
The Christmas season may bring the gift of a bright comet to our skies. Comet Levy (P/2006) should be visible through binoculars and scopes during the latter half of December. This comet was named after David Levy, a well-known and highly respected Canadian astronomer (he has a number of other comets to his credit).
If predictions of its expected brightening hold true, Comet Levy will be visible as a fuzzy glow inside the Great Square of Pegasus - the Winged Horse (of Greek mythology), which sits high in the southwest sky at nightfall. It is expected to brighten further in January.
For the latest update and star map for this comet, check with either www.astronomy.com or www.skyandtelescope.com.
Until next month, clear skies and may your Christmas season be filled with much joy and magic.
Events (AST):
Dec. 2 - First quarter moon; 5:52 a.m.
Dec. 10 - Full moon; 10:36 a.m.
Dec. 14 - Geminid meteor shower peaks
Dec. 17 - Last quarter moon; 8:48 p.m.
Dec. 22 - Winter solstice; 1:30 a.m.
Dec. 24 - New moon 2:06 p.m.
Glenn K. Roberts is a member of the Charlottetown Centre of the Royal Astronomical Society of Canada (RASC). His column appears in The Guardian once a month. He welcomes comments from readers. Anyone who would like to comment on his column is encouraged to email him at glennkroberts@gmail.com.
