The sky in December and January

Mercury is scarcely visible until the last several days of December, when it creeps above the southwestern horizon about half an hour after sunset. During the first half of January, the planet shows up there more clearly near the end of evening twilight. Mercury reaches its greatest eastern elongation from the Sun (19 [degrees]) on January 11, shining at a moderately favorable magnitude of -0.6 but fading rapidly to magnitude +0.3 by the 17th and to +1.3 by the 20th. It then swings down in front of the Sun, reaching inferior conjunction on the 27th.

Venus briefly appears very low in the east-southeast just before sunrise during the first few days of December. It then moves behind the Sun, reaching superior conjunction on January 14, and won't be readily visible again after sunset until at least late February.

Mars moves from Capricornus into Aquarius on December 4, crossing the meridian at about sunset. Look for it in the southwestern sky during the late evening hours. On the 20th, the planet is about 5 [degrees] above the slim crescent Moon; a month later, on the evening of January 18, it returns to a similar position. Throughout January, Mars crosses the meridian about an hour before sunset and is visible low in the southwestern sky until about 10:00 P.M. local time. Indeed, the red planet sets at nearly this hour until the end of May. As of mid-January, Mars is 149 million miles from Earth and thus presents a rather tiny telescopic disk (last June, when it was unusually close to Earth, the planet looked four times as large). Mars gradually fades from magnitude +0.4 on December 1 to +0.8 on January 1 and finally to +1.0 on January 31.

Jupiter, in Gemini, arrives at opposition to the Sun on New Year's Day, shining at a dazzling -2.7 magnitude. In December it rises during evening twilight and remains in the sky all night. By January the planet is already shining in the east when darkness falls; passing overhead before midnight, it sets before sunup. Jupiter is the silvery "star" hovering about 5 [degrees] below and to the left of the Moon on the evening of December 2. The planet is roughly the same distance above and to the right of the Moon on December 30 but appears much closer by January 26.

Saturn, at opposition, is above the horizon from sunset to sunrise on the night of December 3, passing north of the bright orange star Aldebaran. Over the course of the month, it appears to move westward several degrees. Approaching perihelion (on July 26, 2003) with its rings tipped 26 [degrees] to our line of sight, Saturn shines at magnitude -0.5, the brightest it has been in nearly three decades. During January, Saturn is well up in the east-northeast at dusk; by month's end, it sets in the west-northwest at about 3:00 A.M. local time. Observers in the continental United States and parts of southern Canada get to see a nearly full Moon occult Saturn on December 28 at about 4:05 A.M. in the East and at roughly 12:15 A.M. local time on the West Coast. For Hawaii, occultation occurs the previous evening at 8:42 P.M. local time.

The Moon is at last quarter on December 7 at 2:52 P.M. and new on the 14th at 3:47 P.M. First-quarter Moon falls on the 22nd at 3:56 P.M. On December 30 the Moon is full at 5:41 A.M.; a few minutes earlier, the Moon is partially eclipsed, resulting in a brief, slight darkening of its lower rim at 5:29 A.M. In January, last-quarter Moon comes on the 5th at 10:54 P.M., new Moon on the 13th at 8:29 A.M., first quarter on the 21st at 12:46 P.M., and full Moon on the 28th at 5:50 P.M. On January 14 the sliver of a very young Moon hovers less than 6 [degrees] below Mercury in the west-southwest. The following evening, it is well to the east of Mercury and much easier to spot.

The Geminid meteor shower promises a fine display, at least for those willing to brave the chill. These meteors can be seen all night long for a week or so, with no Moon to spoil the view with its glare. Peak activity is expected December 13-14 from evening through morning, when a Geminid meteor should burst across the sky about every minute, especially in the predawn hours. Past displays have featured a richness of both fireballs and faint meteors but have included fewer objects of medium brightness. The meteors appear to originate near the bright star Castor, in Gemini.

The Sun will undergo an annular, or ring-shaped, eclipse on December 14. The eclipse path first strikes Earth over the middle of the Pacific Ocean. Heading east, it passes 300 miles south of the Hawaiian Islands, producing an 84 percent eclipse over Honolulu at 9:27 A.M. Hawaiian time. Veering northeast, the path goes over parts of Nicaragua and Costa Rica, where the Sun will mimic a dazzling ring of fire near sunset. Over most of the United States--except for upstate New York, portions of New England, and Alaska--a partial solar eclipse will be visible. Depending on your location, between 1 and 40 percent of the Sun's diameter may be covered, with the greater coverage visible toward the south. East of the Mississippi River, sunset comes before the eclipse is finished, but the western half of the country has an uninterrupted view.