The Sky In December And January

Natural History, Dec, 2000 by Joe Rao

Mercury is not visible during December, arriving at superior conjunction with the Sun on Christmas Day. But it's a different story in January, when the planet emerges from evening twilight around midmonth, shining very low in the southwest just after sunset. A two-day-old crescent Moon hovers well above and to the right of Mercury on the 26th. The planet reaches its greatest eastern elongation (18.4 [degrees]) on the 28th. On that date, you'll find it far below and to the right of brilliant Venus.

Venus mimics a spectacular "Christmas star" during December, with a dazzling -4.2 magnitude in the southwestern sky at dusk. It sets nearly four hours after sunset. In January the planet reaches its greatest eastern elongation (47.1 [degrees]) on the 17th and continues to brighten. A crescent Moon is in Venus's general vicinity on December 29 and again on January 28.

Mars rises in the east-southeast between 2:00 and 2:30 A.M. Local Standard Time (LST) during December and between 1:30 and 2:00 A.M. LST during January. It continues to brighten slowly as it approaches Earth. On December 20 a fat crescent Moon slides by Mars.

Jupiter and Saturn are visible through much of the night during both December and January. During the first week of December, Jupiter sets at dawn and can be found low in the west-northwest sky. For the rest of the month and throughout January, the planet sets progressively earlier: by the end of December, at about two hours before sunrise, and by the end of January, at about two hours past midnight. Saturn sets about three-quarters of an hour before Jupiter during both months. The two planets continue to provide fabulous viewing through most telescopes. A waxing gibbous Moon forms a wide triangle with Jupiter and Saturn on December 9 and will approach these two planets again on the nights of January 5 and 6.

The Moon in December is at first quarter on the 3rd at 10:55 P.M. The full Moon appears on December 11 at 4:03 A.M., last quarter on the 17th at 7:41 P.M., and the new Moon on the 25th at 12:22 P.M. In January, first quarter is on the 2nd at 5:31 P.M. The Moon is full on the 9th at 3:24 P.M., at last quarter on the 16th at 7:34 A.M., and new on the 24th at 8:06 A.M.

Earth arrives at perihelion, the point of its orbit that brings it closest to the Sun, on January 4 at 4:00 A.M. Earth will be about 91,402,144 miles from the Sun--only about 3.3 percent less than when it's at the far point of its orbit (aphelion) on July 4.

The Geminid meteor shower, usually one of the best meteor displays of the year, is obscured in December by the bright light of the gibbous Moon. The peak night is December 13, continuing into the morning of the 14th. Although up to seventy-five meteors per hour can often be seen during this display, only the brightest meteors will be visible this time.

The winter solstice occurs on December 21 at 8:37 A.M., when the Sun appears to be farthest south of the celestial equator. Winter begins in the Northern Hemisphere, summer in the Southern Hemisphere.

A Christmas Day eclipse, the final one of the second millennium, will be a partial solar eclipse. This event will be visible over nearly all of North America, with the exception of Alaska and the Canadian Yukon and Northwest Territories in the far north and Panama, Costa Rica, and southern Nicaragua in the south. The eclipse can be seen throughout the continental United States and will be in progress at sunrise on December 25 in all of Washington State, most of Oregon, northernmost California, northern Idaho, and northwestern Montana. It will be visible later in the morning in the Midwest, while observers in the eastern states will see it in the early afternoon. Sky watchers across the Great Lakes, northern New York State, and central and northern New England will see at least 60 percent of the Sun's disk covered. Approximately 40 percent coverage will be visible from the northern plains and the central and eastern states. Viewers in much of the Southwest, the south-central states, and Florida will see roughly 20 percent coverage, while those in southwestern Arizona and central and southern California will see even less than that. Remember never to look directly at the Sun unless you are using an appropriate filter to protect your eyes.

A total eclipse of the Moon is staged for the Eastern Hemisphere on January 9. By the time the Moon comes into view in North America, however, the eclipse will be nearing its end. Those living anywhere to the east of an imaginary line extending roughly from Buffalo, New York, to Norfolk, Virginia, will still be able to see some of Earth's dark umbral shadow, which will slip entirely off the rising Moon by 4:59 P.M.

Unless otherwise noted, all times are given in Eastern Standard Time.