FRIDAY, DECEMBER 4
■ Bright Jupiter and Saturn are closer together now (1.8° apart) than modest, 3rd-magnitude Alpha and Beta Capricorni are above them (2.3° apart), as shown below. Wait for full dark to catch the faint stars. Jupiter and Saturn are closing toward their record-breaking conjunction on December 21st, when they will appear only 0.1° apart. That's about the width of a toothpick at arm's length!
SATURDAY, DECEMBER 5
■ Vega still shines brightly well up in the west-northwest after dark. The brightest star above it is Deneb, the head of the big Northern Cross, which is made of the brightest stars of Cygnus. At nightfall the shaft of the cross extends lower left from Deneb. By about 10 p.m., it plants itself more or less upright on the northwest horizon.
■ The waning gibbous Moon rises in the east-northeast around 9 or 10 p.m., close to the Sickle of Leo. By dawn on Sunday morning the 6th the Moon has moved far over to the high southwest, as shown below.
■ The eclipsing variable star Algol should be at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 10:43 p.m. EST.
SUNDAY, DECEMBER 6
■ This is the time of year when M31, the Andromeda Galaxy, passes your zenith after dinnertime (if you live in the mid-northern latitudes). The exact time depends on your longitude. Binoculars will show M31 just off the knee of the Andromeda constellation's stick figure; see the big evening constellation chart in the center of the December Sky & Telescope.
MONDAY, DECEMBER 7
■ Earliest sunset of the year, if you live near latitude 40° north. And why is this, if we're still three weeks from the winter solstice? It's an effect of the tilt of Earth's axis and the eccentricity of Earth's orbit (TW: history and geometry).
This offset from the solstice date is balanced out by the opposite happening at sunrise: The Sun doesn't rise its latest until January 4th.
■ Last-quarter Moon tonight (exactly last quarter at 7:37 p.m. EST). The Moon rises around midnight, below the stick-figure star pattern of Leo. Once the Moon is well up, look to its left for 2nd-magnitude Denebola, Leo's tail-tip. They're about 7° apart (for North America).
Is this your first sighting of Leo this season? By late winter and spring, Leo will be a landmark of the early-evening sky.
TUESDAY, DECEMBER 8
■ As the stars come out, the Cassiopeia W pattern stands on end (its fainter end) very high in the northeast. Watch Cas turn around to become a flattened M, higher in the north, later in the evening.
■ Algol should be at minimum light for a couple hours centered on 7:32 p.m. EST.
WEDNESDAY, DECEMBER 9
■ As Cassiopeia rears very high in the north-northeast after nightfall, the Big Dipper lies shyly down at its lowest 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 in the northeast — while Cassiopeia has wheeled down to the northwest to again stand on end (its brighter end).
THURSDAY, DECEMBER 10
■ The Cassiopeia W hangs very high in the northeast after dark. The bottom star of the W is Epsilon (ε) Cassiopeiae, the faintest. That's your starting point for hunting down the little-known, little-observed star cluster Collinder 463: sparse, loose, subtle, but visible in large binoculars and wide-field scopes on these moonless nights. It's 8° to Epsilon's celestial north (the direction toward Polaris), surrounded by a nice quadrilateral of 4th- and 5th-magnitude stars about 3° wide.
The cluster is nearly 1° long, appearing curved and rather narrow. Its brightest stars are only 8th and 9th magnitude. Use Chart 1 of the Pocket Sky Atlas.
FRIDAY, DECEMBER 11
■ Moon and Venus at dawn. As day begins to break Saturday morning, look southeast for the thin crescent Moon with Venus some 4° or 5° to its lower left (for North America), as shown below. Several hours later the Moon will occult Venus in broad daylight for telescope users in the Pacific time zone. By then the Moon-Venus pair will be getting low in the southwest. Seen from Hawai`i they'll be higher in thinner air. See the December Sky & Telescope, page 50.
SATURDAY, DECEMBER 12
■ Orion comes into view low in the east after dinnertime now, down below the Pleiades and Aldebaran. That means Gemini is also coming up off to its left (for the world's mid-northern latitudes). The head stars of the Gemini twins, Castor and Pollux, are at the left end of the Gemini constellation — one over the other, with Castor on top.
■ If you've been out skywatching lately, you've probably seen a few Geminid meteors by now! The later you watch the better. The shower is due to reach its peak late Sunday night. For much more on the Geminids see the December Sky & Telescope, page 14.
This Week's Planet Roundup
Mercury is lost in the glow of sunrise.
Venus (magnitude –3.9, in Libra) shines low in the southeast during dawn as the "Morning Star." It's a little lower every week.
Very high above Venus, and perhaps a bit left depending on your latitude, shines Arcturus, pale yellow-orange. Look for fainter Spica less far to Venus's upper right.
Mars (about magnitude –0.9, in Pisces) shines bright yellow-orange very high on the southern side of the sky during evening. Mars is fading and shrinking into the distance, but it's still 14 or 13 arcseconds wide in a telescope, big enough to show surface detail during steady seeing. It's gibbous, only 91% sunlit now from Earth's point of view. The recent dust storm activity may be dying down, as suggested by the images below.
To get a (dustless) map of the side of Mars facing you at the date and time you observe, you can use our Mars Profiler. The map there is square; remember to mentally wrap it onto the side of a globe. (Features near the map's edges become very foreshortened.)
Jupiter and Saturn (magnitudes –2.0 and +0.6, respectively) tilt ever farther down in the southwest during and after twilight. Look early. Jupiter is the bright one; Saturn is upper left of it. Watch their separation shrink from 1.8° to 1.1° this week (from December 4th to 11th). Telescopic views will be disappointing, with the planets low in poor seeing.
Jupiter and Saturn will pass just 0.1° from each other at their conjunction on December 21st, low in the sunset. That's about the width of a toothpick at arm's length. The two giants have conjunctions about every 20 years, but this will be their closest one visible in our lifetimes.
Uranus (magnitude 5.7, in Aries) is high in the southeast after nightfall, about 18° east (lower left) of Mars. Uranus is only 3.7 arcseconds wide, but that's enough to appear as a tiny fuzzy ball, not a point, at high power in even a smallish telescope with sharp optics during good seeing.
And while you're there, find the 9th-magnitude asteroid 8 Flora about 10° south (lower right) of Uranus. See Bob King's Tiny Asteroid Flora and Mighty Uranus Team Up, with finder charts and more about both.
Neptune (magnitude 7.9, in Aquarius) is equally high in early evening, over in the south. Neptune is 2.3 arcseconds wide, harder to resolve than Uranus except in very good seeing. Check in on these faint targets when you're done with Mars. Or better yet before Mars. Save that bright night-vision spoiler for last! 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 minus 5 hours. (Universal Time is also known as UT, UTC, GMT, or Z time.)
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 magazine of 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) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to read how to use sky charts with a telescope.
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 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."
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.
"The dangers of not thinking clearly are much greater now than ever before. It's not that there's something new in our way of thinking, it's that credulous and confused thinking can be much more lethal in ways it was never before."
— Carl Sagan, 1996
"Facts are stubborn things."
— John Adams, 1770