The sky in December and January

Natural History, Dec, 2003 by Joe Rao

Mercury sets during twilight in December and is barely visible all month. It passes between the Sun and the Earth on the 26th.

In January, however, the planet puts on an excellent show. Mercury is low in the east-southeastern sky at dawn; look for it an hour before sunrise. Find ruddy Antares in the constellation Scorpius; Mercury is below and to the left of the star, and becomes increasingly distant from it as the month progresses. The little planet shines at magnitude -0.2 between the 17th and the 24th and brightens through the rest of the month. Unfortunately, the early morning is brightening as well, making the planet harder to see.

Venus grows progressively more conspicuous in December, a radiant evening "star" in the southwest visible soon after sunset. For observers at midnorthern latitudes, the planet begins the month less than 15 degrees above the horizon at sunset; by New Year's Eve, though, Venus has shifted to 23 degrees above the horizon at sundown. Binoculars help reveal background stars in the twilit sky as Venus glides past the top of the "teapot" of the constellation Sagittarius during the first third of the month. On Christmas night a slender crescent Moon and Venus make for an eye-catching celestial tableau.

In January, Venus, gleaming at magnitude -4, ascends dramatically higher, its sunset altitude increasing to 33 degrees by month's end. Seen through a telescope, Venus wanes from nearly full to more definitely gibbous. But the naked-eye view of the planet streaking across hall of Capricornus and most of Aquarius as the month progresses is the really exciting spectacle. On the 24th Venus and the crescent Moon virtually replicate their Christmas-night encounter.

Mars, fading after its autumnal glory, is near its highest point in the sky at evening twilight and sets at about midnight. In December the planet, shining south of both Pisces (the fishes) and the square of Pegasus (the winged horse), progresses 15 degrees eastward relative to the two constellations. On the 1st Mars is 79 million miles from Earth and shines at magnitude -0.4; by New Year's Day the planet has receded 25 million miles more, and dimmed to magnitude 0.2.

Mars declines in brightness again, by another hall a magnitude, during January, as the Earth's smaller orbit further separates the planets. On the evening of the 27th Mars hovers above a fat crescent Moon.

Jupiter rises in the east just after midnight as December begins, and at about 10:15 P.M. by month's end. It's shining brilliantly at magnitude -2.1 all month in the constellation Leo (the lion)--about 18 degrees east of Regulus, Leo's brightest star, at midmonth. Regulus precedes Jupiter on their way up the sky by about ninety minutes, but the giant planet is well worth waiting for: even when Jupiter is low in the sky, its four bright moons present an ever-changing dance for the telescope.

In January giant Jupiter rises four minutes earlier with each passing night, and comes up just after 8 P.M. local time by month's end. The planet rises practically due east, and so climbs the sky rapidly as the evening passes--more than 20 degrees in less than two hours. By the end of January it reaches its highest point around 2:30 A.M.

In December Saturn makes its finest apparition in thirty years. It arrives at opposition to the Sun on New Year's Eve, rising as the Sun sets, reaching its highest point in the southern sky at midnight, and setting as the Sun rises. It is also closer to Earth on this night (748.3 million miles) than it has been since another, similar opposition in December 1973. Because of its unusual proximity, Saturn shines as bright as it can ever get: magnitude -0.5. Not until January 2034 will the planet repeat this year's spectacular show. Its rings are dramatically tipped more than 25 degrees to out line of sight: a certain delight for anyone lucky enough to receive a telescope as a holiday gift.

In January Saturn is already well up in the east at sundown and sets in the west-northwest an hour or two before sunrise. The Moon passes to the north of Saturn on the evening of the 6th.

The Moon waxes full on December 8 at 3:37 P.M. It wanes to last quarter on the 16th at 12:42 P.M. and becomes new on the 23rd at 4:43 A.M. It waxes to first quarter on the 30th at 5:03 A.M.

In January the Moon waxes full on the 7th at 10:40 A.M. It wanes to last quarter on the 14th at 11:46 P.M. and becomes new on the 21st at 4:05 P.M. It waxes to first quarter on the 29th at 1:03 P.M.

The Gemenid Meteor Shower should entice even those observers faced with mid-December cold. Now considered the richest of the annual meteor showers (surpassing even the celebrated Perseids of August), the show should peak on the night of December 13-14. You might see as many as 120 "shooting stars" an hour--but expect considerable intefference from a waning gibbous Moon toward morning, when the meteor rates are highest.

The solstice takes place at 2:04 A.M. on December 22. Winter begins in the northern hemisphere; summer begins in the southern.