The Sky This Week, 2012 December 11 - 18
Full Moon and Jupiter, 2012 November 28
The Moon returns to the evening sky this week, emerging in the southwestern sky as twilight falls on the 14th before wending her way through the dim stars of the autumnal constellations. New Moon occurs on the 13th at 3:42 am Eastern Standard Time, so her slender crescent should be fairly easy to spot after sunset on the 14th. Luna will be a few degrees west of ruddy Mars at this time, and you may wish to have a pair of binoculars handy to spot the red planet in the twilight glow.
Those of you who don’t like the early onset of night take heart; the earliest sunsets of the year are now behind us. This week Old Sol gradually begins to set a bit later. You probably won’t notice at first, but by Christmas you’ll have five more minutes of daylight than we do right now. However, this is balanced somewhat by the time of sunrise, which continues to move later in the morning. Our latest sunrise won’t occur until January 4th. Sandwiched in between is the Winter Solstice on the 21st, which marks the shortest day of the year. The seeming discontinuity of sunrise, sunset, and solstice times derives from several factors but mostly falls on our need to observe "standard" time, which generally doesn’t mirror what the Sun is actually doing in the sky. A very thorough explanation of the "Dark Days of Winter" can be found here on our website.
The timing of the New Moon offers us a perfect circumstance to take in the annual Geminid meteor shower. This display of celestial fireworks is one of the most consistent performers of all the annual showers, but it doesn’t get as much attention as the August Perseids even though it almost always outperforms them. The reason for this is fairly simple. Meteor watching is a very sedentary activity; my typical setup is a lawn chair in the back yard and a can of mosquito repellant. For the Geminids the bug spray won’t be necessary, but lots of warm clothes and/or blankets are a must! Yes, lying on your back looking up in the wee hours is a fine activity in August, but you’ll quickly learn just how cold you can get doing the same thing in December! However, the effort is well worth it, as the Geminids consistently perform quite admirably. The shower’s radiant is near the star Castor in Gemini, which rises well before midnight. This is one of the few showers that you don’t need to get up at "oh-dark-thirty" to view; the best viewing time should be between 10:00 pm on the 13th and around 2:00 am on the 14th. A single observer in a dark location can expect to see up to 50 meteors per hour, while urban skywatchers may see 25 to 30 per hour. The Geminids are much slower than the Perseids, and brighter ones will travel across a good swath of sky before they burn out, often leaving a faint smoke train from their passage. You can also catch a few on the nights before and after the peak, but the night of the 13th – 14th is the "bulls-eye". So bundle up, make a thermos of hot coffee or cocoa, and set up your lawn chair with your feet pointing east in as dark a place as you can find, and enjoy the show. As the night passes by, take some time to admire the bright stars of the Great Winter Circle. They might not warm you up, but they will certainly brighten your night.
As mentioned earlier, Mars still hangs tough in the southwestern sky at dusk. The Moon will be nearby on the evening of the 14th, and the red planet will continue to linger in this part of the sky through the end of the year.
Jupiter now dominates the evening sky from sunset to sunrise. You will notice him in the east almost as soon as the Sun goes down, and by the late evening he is nearly overhead, beaming down with a bright golden glow. He is prominently featured on the western perimeter of the Great Winter Circle, just under five degrees away from the reddish-hued star Aldebaran. Owners of telescopes of six inches or more in aperture should look for the Great Red Spot crossing the planet’s disc on the evenings of the 14th and 16th. On the latter evening you may also spot the shadow of the Galilean moon Io transiting the disc on the Red Spot’s northern boundary. There is always something going on at this wonderful planetary system!
Early risers can still catch a glimpse of fleet Mercury just above the eastern horizon about an hour before sunrise during the first few days of the week. Dazzling Venus will be just over six degrees away, higher up and to the right. Mercury should be visible to the unaided eye if you have a very flat horizon, but a pair of binoculars will be very helpful if you have to peer through any horizon haze. By the week’s end the fleet planet will be much harder to spot, so try for him now. Venus should be easy to find throughout the week, and yellow Saturn shines some 16 degrees above Venus with the star Zubenelgenubi placed about mid-way between.