Friday, Dec. 6
• The Moon shines lower left of the Great Square of Pegasus.
• Gulf Coast asteroid occultation tonight. David Dunham of the International Occultation Timing Association (IOTA) writes, "One of the brighter asteroidal occultations of the year will occur just before 11 p.m. CST across southern Texas, just south of New Orleans, and over Jacksonville, Florida. This will be the occultation of 6.5-magnitude 18 Aurigae by the 72-km asteroid 55 Pandora. Clear skies are predicted for southern Texas, and it may be clear enough to observe it from Jacksonville as well." Further details can be found on IOTA's webpage.
Saturday, Dec. 7
• Vega is still the brightest star in the west-northwest in early evening. The brightest over it is Deneb. Farther to Vega's left is Altair, midway in brightness between Vega and Deneb.
These three form the Summer Triangle, and when the Summer Triangle finds itself here, you can look for the Great Square of Pegasus crossing the meridian high in the south.
• Earliest sunset of the year today and tomorrow, if you live near latitude 40° north. Even though we're still two weeks from the winter solstice.
This offset of the earliest sunset from the solstice date is balanced out by the opposite happening at sunrise: The Sun doesn't come up its latest until January 4th. Why? Blame the tilt of Earth's axis and the eccentricity of Earth's orbit.
Sunday, Dec. 8
• Orion fully clears the eastern horizon by 7 or 8 p.m. now, depending on how far east or west you live in your time zone. High above Orion shines orange Aldebaran. Above Aldebaran is the little Pleiades cluster, the size of your fingertip at arm's length.
Far left of Aldebaran and the Pleiades shines bright Capella.
Down below Orion, brilliant Sirius now rises around 8 or 9.
Monday, Dec. 9
• At this time of year the Big Dipper lies down lowest soon after dark, due north. It's entirely below the north horizon if you're as far south as Miami.
But by midnight, the Dipper stands straight up on its handle in fine view high in the northeast!
Tuesday, Dec. 10
• Venus and Saturn are just under 2° apart in late twilight this evening and tomorrow evening. Look rather low in the southwest. Although they appear close together, Saturn is actually 8 times farther away. And it's 10 times larger in diameter, though it's much less brightly lit by the distant Sun.
Wednesday, Dec. 11
• Full Moon tonight (exact at 12:15 a.m. EST), shining in eastern Taurus. In the evening look for orange Aldebaran to the Moon's right, the Pleiades peeking through the moonlight above Aldebaran, and brighter Capella farther to the Moon's upper left. Betelgeuse, in Orion's shoulder, is down below.
By midnight the Moon is very high in the south, not far from the zenith. The full Moon of the Christmas season rides higher across the sky at midnight than the full Moon in any other season, thus "giving lustre of midday to objects below."
• Just before the beginning of dawn Thursday morning, find Mars, a mere magnitude 1.7, low in the southeast. It's only 1/4° or less from Alpha Librae (Zubenelgenubi), which is not that much fainter at magnitude 2.8. Binoculars can show that Alpha Librae is a wide double star: the secondary, magnitude 5.1, glimmers 1/15° above the primary.
Thursday, Dec. 12
• The Summer Triangle is sinking lower in the west, and Altair is the first of its stars to go (for mid-northern skywatchers). Start by spotting bright Vega, magnitude zero, in the northwest right after dark. The brightest star above Vega is Deneb. Altair, the Triangle's third star, is farther to Vega's left or lower left. How late into the night, and into the advancing season, can you keep Altair in view?
Friday, Dec. 13
• The Geminid Meteor shower, usually one of the best of the year, should be at its peak late tonight and tomorrow night. But the waning gibbous Moon will light the sky, so only the brightest few meteors will shine through. You might see one every several minutes on average from midnight to dawn, if you have a wide-open view of the sky overhead and shield the glary Moon from your eyes.
In early evening the meteors will be much fewer, but the Moon will be lower — and the Geminids that do appear will be long Earth-grazers skimming far across the top of the atmosphere.
Saturday, Dec. 14
• The waning gibbous Moon, in Gemini, rises after dinnertime below Pollux and Castor. To the lower right of the Moon, Procyon is soon on the rise. Off to the right of Gemini sparkles Orion.
Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.
This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.
Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.
Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) and Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.
You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.
Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning really heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."
This Week's Planet Roundup
Mercury, magnitude –0.6 all week, gradually moves lower in early dawn this week. Spot it low in the east-southeast about 40 minutes before sunrise. Look for it very far below Arcturus and perhaps a little to the right (depending on your latitude).
Mercury is lower left of fainter Mars and Spica.
Mars (magnitude +1.7, in Libra) is low in the east-southeast in early dawn, to the upper right of Mercury. Brighter Spica shines farther upper right of Mars. This long line of three expands from 33° to 43° in length this week, as Mercury sinks lower and Mars and especially Spica move higher.
Venus (magnitude –3.9, in Sagittarius) shines in the southwest in evening twilight, a little higher each week now. It's on its way up to a grand, high "Evening Star" apparition all this winter and well into spring. In a telescope it's small and gibbous, since it's nearly on the far side of the Sun from us.
Jupiter (magnitude –1.8) moves farther to the lower right of Venus in twilight and becomes ever trickier to spot before it sets. The gap between them increases from 13° to 20° this week.
Saturn (magnitude +0.6, also in Sagittarius) is the modest, steady yellow "star" near Venus — which outshines it by 60 times! Find Saturn 5° to Venus's upper upper left at the beginning of the week, and 7° to Venus's right or lower right at week's end.
They're in conjunction, just under 2° apart, on December 10th and 11th.
Uranus (magnitude 5.7, in southern Aries) and Neptune (magnitude 7.9, in eastern Aquarius) stand about equally high in the south and southeast, respectively, right after dark. Use our finder charts for Uranus and Neptune.
All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.
Eastern Standard Time (EST) is Universal Time (UT, UTC, GMT, or Z time) minus 5 hours.
Audio sky tour. Out under the evening sky with your earbuds in place, listen to Kelly Beatty's monthly podcast tour of the heavens above. It's free.