Magazine article Natural History

The Sky in December and January

Magazine article Natural History

The Sky in December and January

Article excerpt

Just before sunrise from December 7th until the 14th, Jupiter (magnitude -1.7). Mercury (-0.6), and Mars (1.5) cluster low in the east-southeast sky. The best time to look for this intriguing pre-Christmas gathering is around 6:30 A.M. local standard time-though the group's low altitude and proximity to the Sun will probably make it impossible (or nearly so) to see Mars with the unaided eye. The trio becomes most compact on the 10th-the three planets fit inside a one-degree circle. On that morning, they resemble a small arrowhead pointing west, with Mars at the tip of the arrow.

By the 20th, Mercury is rising even later, just forty-five minutes before the Sun does, and so it becomes hard to see. The planet reaches superior conjunction, behind and roughly in line with the Sun, on January 7th, and then bolts back into view late in the month in the evening sky. By the 27th you might glimpse Mercury with the naked eye low in the southwest, between about thirty and forty minutes after sundown. Use Venus as a guide; you will see Mercury about eight degrees below and to the right of the bright planet (your clenched hst held at arm's length measures roughly ten degrees of arc).

During December Venus begins to climb up out of the sunset's glow in earnest and returns, at magnitude -3.9, to reclaim its role of brightest evening "star." Look for Venus with binoculars shortly after sundown very low in the southwest. Un December 1st the planet is just four degrees above the southwest horizon at sundown (as seen from around forty degrees north latitude); it touches the horizon about a half-hour later.

By New Year's Day Venus is eleven degrees high at sunset and remains up tor more than an hour, dome the end or January, this interval increases to almost two hours, and Venus is still about nineteen degrees above the horizon at sunset. Don't expect any good telescopic views of the planet just yet, though. Even with good magnification, Venus remains a dot of dazzling light, just barely out of round.

From late December until next May Mars rises soon after the beginning of morning twilight. On New Year's Day, when it lies 222 million miles from the Earth, Mars is a dim, +1.5-magnitude object low in the southeastern sky. That makes it somewhat fainter than the ruddy star Antares, which is nearly ten degrees above the Red Planct and to Us right in the constellation Scorpius, the scorpion. During January the planet moves twenty-four degrees eastward, from the constellation Ophiucluis. the serpent holder, into the constellation Sagittarius, the archer. In fact, Mars nearly keeps pace with the Sun. With a large telescope, you might be able to resolve the planet into a tiny disk.

By the end of December, Jupiter is rising a few minutes before 5 A. …

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