Feature Article December 4, 2002
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Five Bright Planets and a Meteor Shower
At this latitude, the latest sunrise of the year does not occur until Jan. 3. The most southerly positions of the sun as it rises and sets are on December 21, the date known as the Solstice.
The December Full Moon on December 19 appears further north and higher in the sky than any other Full Moon of the year. That night you may watch the moon rise in the northeast, and later appear almost straight overhead by midnight, and later still, as morning approaches, see it setting in the northwest.
This month the great winter constellations feature more bright stars than at any other season. Foremost among them is the large distinctive constellation, Orion the Hunter, marching across the southern sky followed by his dogs, Canis Major and Canis Minor. The big dog has the star Sirius, brightest star in the whole sky, marking its eye. The smaller dog nearby has the star Procyon, the skys sixth brightest star, to mark its location. Orion himself has very bright stars to mark his shoulders, knees and waist, some of them almost as bright as the dog stars. Three distinctive stars of almost equal brightness and in a straight line form Orions Belt. Orion is well up in the southeast by 8 p.m., and his two dogs are easy to see in the same direction by 10 p.m.
At this time of year, try to notice that the bright stars of Cygnus, which were within the Summer Triangle and appearing like a great bird flying overhead in the late summer evenings, are now standing upright, throughout the December evenings, on the northwestern horizon, clearly showing why this constellation was called The Northern Cross, a symbol appreciated at Christmas time by mediaeval Christians.
All five of the bright planets that can be seen with the unaided eye will be easily visible this month. Saturn is perfectly placed this month for observing and studying it all night. Low in the east after sunset, it is to the left of the star pattern called the Hyades which forms the Head of the Bull, Taurus, and located near the star that marks the end of one of the horns, the planet seems to be caught on the horns of Taurus. Jupiter, the brightest planet of the evening sky, rises in the east before 10:00 p.m. in early December and before 8:00 p.m. in late December. This largest of the planets is seen between the constellation Cancer, the Crab, which is on its right and Leo, the Lion, with the very bright star Regulus, which is on its left. Over the course of the month, both Saturn and Jupiter move very slightly to the right, as seen against their background stars. During the last half of the month, Mercury may be seen, for about a half-hour to an hour, low in the south-western sky beginning about a half-hour after sunset. In the morning sky for about two to three hours before sunrise, there is also a fine planetary display. Both Venus and Mars rise in the southeast over three hours before sunrise. Venus is a spectacular sight because of its amazing brilliance. Reddish Mars is easily found above it and slightly to the right, though it is many times fainter. Both of these planets are just below, and to the left of, the whitish star Spica, brightest star in the constellation Virgo. As the month progresses, try to observe the movement of Venus as its orbit takes it closer to, and then away from Mars. Another interesting experiment is to try to see if you can follow Venus for several hours and still see it after sunrise. The easiest way to locate it is just to follow it from twilight and past the time of sunrise.
The moons monthly orbit will take it past several planets. On the nights of Dec. 18 and 19, watch the moon as it moves in relation to the planet Saturn. On the nights of Dec. 22 and 23, watch as it moves past the planet Jupiter. In the early morning of Dec. 30, the moon will form a beautiful triangle with Venus and Mars in the south-eastern sky, 90 minutes before sunrise.
December is the month for the Geminid Meteor Shower, which is often one of the best of the year. If weather permits, this shower should produce more visible meteors than were seen by local observers looking for Leonid Meteors last month, when I was appalled by the false expectations created in several newspapers by writers who simply failed to investigate the meaning of the Zenithal Hourly Rate, which they quoted as being from 3000 to 10000 per hour, without bothering to state that these numbers decreased by over 90% because of each of the limiting factors: (1) the Full Moon, (2) the meteor radiant being near the horizon, (3) and the light pollution, to say nothing of air pollution, haze and scattered cloud. The arithmetic would have shown them that the expected numbers should have been 10 to 20 per hour!! For the Geminids, the moon will not be a factor, IF OBSERVERS WAIT UNTIL AFTER MOONSET, on the night of the peak, December 13-14. Moonset locally that night is at 2:16 a.m. Although the Z.H.R. for this shower is given as 95 per hour (and doubtless, a few newspaper writers will find that number somewhere and quote in their columns), observers should expect to see 5 to 10 per hour if they observe BEFORE moonset and 50 to 60 per hour AFTER moonset, IF they have clear skies and can totally avoid light pollution, haze, and scattered cloud. Try to observe from moonset at 2:16 a.m. until twilight begins at 5:49 a.m.; if you can find a spot away from light pollution, you may be very impressed with the number of shooting stars that you see in the southern sky. Geminids are among the slowest of the meteors that burn up in our atmosphere; at 35 kilometres per second they are travelling at only half the speed of the particles in the Leonid Shower of last month. Some meteors may be seen on several nights both before and after the peak. I look forward to hearing from readers about hourly counts of Geminids.
More information is to be found in The Beginners Observing Guide, available at Sharbot Lake Pharmacy. It could be a suitable Christmas gift. I wish all readers a safe and happy Christmas holiday!
