Skylog

Natural History, Dec, 2008 by Joe Rao

On December 5 Mars arrives at conjunction with the Sun (whenever the two conjoin, Mars is behind the Sun from our viewpoint--only Mercury and Venus can also pass in front of the Sun). The Red Planet got increasingly lost in the solar glare starting in October, and we will be lucky to glimpse it again before April. But four other planets perform for us.

Venus soars to prominence in the southwest during December and January. If the air is clear and the sky deep blue, try looking for the planet shortly before sunset. Venus sets nearly three hours after the Sun on December 1, and lingers for almost four hours by New Year's Eve.

Jupiter starts December near Venus but then moves in the opposite direction. Each evening it sets earlier, so by month's end it is descending deep into the glow of sunset. In January, as the planet approaches its conjunction with the Sun on the 24th, it is too close to the Sun to observe properly.

Mercury reaches its greatest eastern elongation, 19 degrees east of the Sun, on January 4. That provides for a moderately favorable apparition, but the planet fades rapidly thereafter, reaching inferior conjunction (passing in front of the Sun) on January 20.

Saturn rises in the east around 12:30 A.M. local time on December 1 and is in excellent position for observation as morning twilight begins. Rising four minutes earlier each night, it will already be above the eastern horizon by 8:30 P.M. near the end of January. The planet slows to a stop on New Year's Eve, and then appears to move westward (retro grade) against the background stars until May 17, when it turns eastward (direct) again.

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DECEMBER NIGHTS OUT

1 Venus, Jupiter, and the crescent Moon are clustered closely together--within a 5-degree field--in the south-southwestern sky. The trio forms a triangle, with Jupiter and the Moon in the top corners and Venus at the bottom. It's a gorgeous sight!

5 The Moon waxes to first quarter at 4:26 P.M. eastern standard time (EST).

12 The Moon becomes full at 11:37 A.M. EST. On this day the Moon is also at perigee, its point in orbit closest to Earth.

Moreover, this month's perigee is the closest one for 2008 (perigee varies by about 8,700 miles). The consequence will be a full Moon that is larger and slightly brighter than average, and unusually high and low tides around this date.

13 Just past full, the Moon casts a bright pall over the peak night of this year's Geminid meteor shower. The emanation point (called the "radiant") for those meteors is in the constellation Gemini, the Twins, near the star Castor, which sits high in the sky not long after midnight. Even in moonlight, a Geminid fireball can be bright enough to attract attention.

19 Saturn is 7 or 8 degrees above and to the left of the Moon as they ascend the eastern sky in the wee hours of this day. The Moon wanes to last quarter at 5:29 P.M. EST.

21 The Sun reaches its southernmost position (since the Earth's north pole is maximally tilted away from it) and begins to return northward. The solstice occurs at 7:04 A.M. EST; winter begins in the Northern Hemisphere, and summer in the Southern.

27 The Moon is new at 7:22 A.M. EST.

28 About a half hour after sunset, using binoculars, you might glimpse a very thin crescent Moon near the southwest horizon, with Mercury and Jupiter both hovering several degrees above and to its left. The Moon will be much easier to spot the following evening, having left the two planets to its lower right.

31 Look for Jupiter and Mercury side by side, beginning about a half hour after sunset, low in the southwestern sky. Jupiter, on the right, is the brighter of the two. Much higher up in the south-southwest, Venus shines below and to the left of the Moon. You won't notice it, but a leap second will be added just before the clock strikes 7 P.M. EST.

JANUARY NIGHTS OUT

4 The Moon attains first quarter at 6:56 A.M. EST. Mercury is at its greatest eastern elongation, 19 degrees east of the Sun. The planet sets in the west-southwest some minutes before the end of evening twilight.

10 The Moon becomes full at 10:27 P.M. EST.

14 Venus is at its greatest eastern elongation, 47 degrees east of the Sun; viewed through a telescope it appears half lit. Ascending the eastern sky during the late evening hours is Saturn, about 6 degrees to the left of the Moon.

17 The Moon wanes to last quarter at 9:46 P.M. EST.

26 The Moon becomes new at 2:55 A.M. EST. An annular (ring) eclipse of the Sun occurs over the Atlantic and Indian Oceans; only near the end of its track does the Moon's antumbra (as the annular shadow is called) finally score a landfall--over Sumatra, Java, and Borneo.

29-30 The crescent Moon slides past Venus: in the early evening of the 29th it is situated below and to the planet's right, while on the 30th it is high above Venus.

JOE RAO (hometown.aol.com/skywayinc) is a broadcast meteorologist and an associate and lecturer at the Hayden Planetarium in New York City.