Night Skies: Moon, Venus, Jupiter In Tight Company Tonight

There's no need to wait for this month's celestial highlight; get outside tonight an hour after sunset, and look to the southwest. There, low on the horizon, the crescent moon forms a tight triangle with Venus and Jupiter. But don't delay: It's a one-night show and lasts only a couple of hours before Venus, the lower planet, leads the others below the horizon. By Tuesday night, the moon will have moved away to the upper left. It's an uncommonly close grouping of the three brightest objects in the night sky, and we're fortunate it occurs in the moon's crescent phase. A fuller moon would detract from the planets' brilliance. Venus, seemingly stuck just above the horizon for a couple of months, finally gains altitude in December, ending the month a third of the way up the sky, still in the southwest. Jupiter, though, is headed downward. The big planet will be half as high by Dec. 31, when it has its second close encounter of the month.
Mercury rises quickly during December. On Dec. 28, it will be half as high and just below Jupiter. You might be able to make out an ever-so-slender crescent moon even lower; binoculars may be needed to see it in the post-sunset glare. Mercury meets up with Jupiter on New Year's Eve, when the solar system's largest and smallest planets (sorry, Pluto) will appear just 1.3 degrees apart, closer than Venus and Jupiter are tonight and about the width of your pinkie held at arm's length. Look around 5:15, 45 minutes after sunset. Above them to the left, Venus seems a brilliant pendant dangling from the lower cusp of the crescent moon. Saturn rises now just after midnight, and at dawn is high in the south. It's up two hours earlier by month's end. Mars, which disappeared into the sunset just as autumn began, is in conjunction with the sun on Friday, lying directly on the other side from us. The moon is full Dec. 12 — terrible timing for the Geminid meteor shower, which peaks the next night. As it did to the Orionids in October and the Leonids last month, the bright moonlight will make it hard to see all but the very brightest meteors. They will appear to originate from the constellation Gemini, not far from the moon, and may be seen beginning around 10. Good luck. Tonight, however, the moon will be down early, and you might be able to see a changing of the guard. You'll have to have a good view of the horizon all around, or be on a hilltop. Right around 9 p.m., the stars of the Summer Triangle will be about to set. Just above the western horizon is Altair; Vega is not much higher in the northwest, with Deneb above it. Obviously, this asterism is named for the season in which it is most prominent high overhead. Now look all the way across the sky. Very low in the east-southeast, our brightest star, Sirius, is rising. Due east and very low is Procyon in Canis Minor (the Little Dog). Along with Betelgeuse, the prominent red star above them in Orion, they form the Winter Triangle. It will be at its highest in the depths of winter. Speaking of which: At 7:04 a.m. on Dec. 21, we reach the solstice, the moment at which the Earth's axis is pointed away from the sun in the Northern Hemisphere and the start of our winter. The night of Dec. 20-21 is the longest of the year, and the 21st is the shortest day. Note the sun's position: It's as low as it gets in the southeast at sunrise and in the southwest at sunset. And it will be much higher before our weather gets much warmer.