December opens with the moon at first quarter Dec. 2, meaning it is seven days (and a little bit) from new. Seven days (and a little bit) later will be full moon, and this particular full moon Dec. 10 lines up with the Earth's shadow - a lunar eclipse, which will be visible from most of North America.
The eclipse will still be in its central phase as the moon sets in the west at sunrise. A few days earlier, Dec. 6, Jupiter will be within a few degrees of the moon; Dec. 17, eight degrees north of Mars; Dec. 20, seven degrees north of Saturn; Mercury three degrees north Dec. 23; new moon Dec. 24; and Venus within six degrees Dec. 27.
Mercury will be in front of the sun (inferior conjunction) in the early part of the month, and will begin showing up in the eastern early morning by mid-December.
Venus is that bright light in the south western horizon at dusk. Watch for a thin crescent moon hovering nearby Dec. 26 and 27.
Mars rises in the east shortly after midnight, and fades away in the bright early morning daylight. The Red Planet appears tiny compared to Venus and the gas-giant planets; it's a long way off yet, making its closest approach in early March 2012.
During December, Mars averages 1.2 astronomical units away from Earth - a little more than our distance from the sun. To get a feel for how large Mars appears, consider that the moon is a half a degree in diameter, where Mars displays an angular size of nine arcseconds. Even though Mars is actually twice the diameter of the moon, distance is everything; the moon's apparent half degree equals 30 arcminutes, or 1,800 arcseconds - appearing 200 times larger than Mars.
Jupiter is well placed during December for evening viewing, continuing in retrograde motion (westward) until Dec. 26, when it appears to stop and then begin moving eastward again. Don't forget that it's us doing the moving, rounding our orbit much more rapidly than Jupiter - 12 times faster, in fact.
Get out the binoculars or a small telescope to watch the daily dance of the Galilean moons, and watch the planet slowly spin on its axis. Over the course of a couple of hours, Jupiter revolves considerably - quite noticeable to the observant eye.
Saturn rises in the east in the early morning hours, hovering all month near the bright star, Spica, and then the Ringed Planet gets quickly swallowed up in the sun's glare. Watch for a waning crescent moon nearby Dec. 19 and 20.
Uranus and Neptune rise during daylight and set near midnight in the west.
- James Edgar has had an interest in the night sky all his life. He joined The Royal Astronomical Society of Canada in 2000. He is editor's assistant and a contributor to Observer's Handbook, production manager of the bi-monthly RASC Journal and is the society's national secretary.
