The Sky In December And January

Natural History, Dec, 1999 by Joe Rao

Mercury is best viewed during the first week of December, as it reaches its greatest western elongation on the 2nd. Rising at about 5:30 A.M. in the east-southeast, it hovers roughly halfway between brilliant Venus and the horizon by sunrise.

Venus continues to dazzle in the predawn sky during December and January. The crescent Moon will be in its vicinity on the mornings of December 2 and 3 and again on January 3.

Mars can be found low in the southwest at dusk through December and January. It will set at about 8:30 P.M. Look for it shining close to the crescent Moon on the evening of January 10.

Jupiter and Saturn are spectacular in our early-evening winter skies, shining high in the south at dusk and not setting until well past midnight. Brilliant Jupiter recently passed its best opposition in its dozen-year orbit. Its four largest moons (Io, Europa, Ganymede, and Callisto) are a telescopic treasure; they run a merry race with one another and change their respective positions from hour to hour and from night to night. Just to the east of Jupiter is Saturn, shining more brightly than it has since the mid-1970s. Its icy rings fascinate even experienced observers. Any telescope with a 30x or greater magnification will show them. The gibbous Moon will be close to Jupiter late on the night of December 17 and near Saturn late the following night.

The Moon is new on December 7 at 5:32 P.M. December's first quarter is on the 15th at 7:50 P.M., and full Moon is on the 22nd at 12:31 P.M. At a distance of only 221,624 miles, this is also the full Moon closest to Earth in 1999, so tides will be much higher than normal. Last quarter is on December 29 at 9:04 A.M. In January, new phase is on the 6th at 1:14 P.M., first quarter is on the 14th at 8:34 A.M., full Moon is on the 20th at 11:40 P.M., and last quarter is on the 28th at 2:57 A.M.

The Geminid meteor shower reaches its peak on the night of December 13. Under ideal sky conditions, slow, graceful meteors can be seen at a rate of approximately a hundred per hour. These are often called the best of the annual meteor showers, surpassing even August's Perseids. After the nearly first-quarter Moon sets, at about 9:40 P.M. Monday evening, a fair number of meteors should be visible. They will appear to emanate from the star Castor in the Gemini constellation. The very best time to watch is at about 2:00 A.M., when Gemini is almost directly overhead.

The winter solstice occurs at 2:44 A.M. on December 22--the same day, interestingly enough, as the perigee full Moon. Winter begins in the Northern Hemisphere, summer in the Southern Hemisphere. During the first moments of January 3 (12:00 A.M.), Earth will be at the perihelion, its closest point to the Sun, at a distance of 91,405,304 miles.

A total eclipse of the Moon will take place on the night of January 20, making this the first opportunity since 1993 for North Americans to see one. The eclipse will be visible to all regions of the globe that are turned toward the Moon during the time the eclipse is in progress; this includes the entire Western Hemisphere as well as Europe, western Asia, and most of Africa. Sunlight, refracted by Earth's atmosphere, takes on a reddish sunsetlike tint. This red light always falls onto the Moon when it is full, but the bright reflected light of the Sun overwhelms the faint red hue, so we usually can't see it. When the Moon moves into total eclipse, however, the red light suddenly becomes its only illumination; hence, the Moon appears to light up like a coppery ball at and near the eclipse's totality. The Moon will enter Earth's umbral shadow at 10:01 P.M. and become totally immersed by 11:04 P.M. Mid-totality comes at 11:44 P.M., totality ends at 12:22 A.M., and the Moon will be completely free of the umbra at 1:26 A.M.

All times are in Eastern Standard Time.