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!

Getting closer... Jupiter and Saturn now appear closer together than Alpha and Beta Capricorni above them.

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.

Moon and Sickle of Leo at dawn, Dec. 6, 2020
As dawn begins to break on Monday the 6th, the waning gibbous Moon forms a flattish, isosceles triangle with Regulus and orange Algieba (Gamma Leonis) for skywatchers in North America.

■ 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.

The waning Moon in the dawn passes Venus on Saturday the 12th.

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.

Advertisement


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.

Mars on November 21st, imaged by Christopher Go. South is up. The striking dark diagonal streak at left is part of Sinus Sabaeus reframed by dust clouds. In the upper center "the region around Mare Erythaeum is covered with dust," writes Go. "Even Sinus Meridiani [lower left of center] is shrouded in dust. The eastern part of Sinus Sabeaus is dust free, but the area attached to Meridiani has dust going through! This region of Mars is unrecognizable!"
The Syrtis Major side of Mars as imaged by Go eight days later, on November 29th. South is up. Syrtis Major is the large dark peninsula pointing down. The darkest horizontal band at right is Sinus Sabaeus, now looking more like its normal self. Between Syrtis Major and the South Polar Cap at top, the Hellas Basin is bright. Dust activity seems to continue there.

Go lives in the Philippines, on the opposite side of Earth from North America. Therefore his evening observing hours when Mars is high are about 12 hours out of sync with ours. Mars also rotates about once every 24 hours, so we see the opposite side of Mars that he does.

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.

Pocket Sky Atlas cover, Jumbo edition
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown here is the Jumbo Edition, which is in hard covers and enlarged for easier reading outdoors at night. Sample charts. More about the current editions.

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.

You'll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger (and illustrated) 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 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

 


Comments


Image of Rod

Rod

December 7, 2020 at 8:20 pm

Observed 1700-1730 EST. I did some prep work for the very close conjunction of Saturn and Jupiter coming on 21-Dec-2020. Saturn and Jupiter easy to see, well above the tree line in SW in my field. I used an older 40-mm plossl for 25x, wide field view with the 90-mm refractor telescope. Both planets just fit into the FOV. At 25x I could see some cloud belt on Jupiter, 3 Galilean moons on one side, another Galilean moon on the other side. Saturn rings just visible and Titan distinct. This was a fun test. If weather permits perhaps I can get a very good view of Saturn and Jupiter about 6 arcminute angular separation on 21-Dec near 1700 EST/2200 UT. Tonight they were about 1.5 to 1.6 degrees apart or 91-92 arcminute. As Saturn and Jupiter get closer and closer this month for their conjunction, perhaps someone will get a very good photo. The pairing begs for some good pictures 🙂

You must be logged in to post a comment.

Image of mary beth

mary beth

December 8, 2020 at 11:47 am

The preparation and anticipation are part of the fun aren’t they! It looks like a few days before and after will be almost as spectacular. Looking forward to the photos as well. Are you going to have your neighbors over for the viewing ?

You must be logged in to post a comment.

Image of Rod

Rod

December 8, 2020 at 12:15 pm

mary beth, no special plans for 21-Dec when Saturn and Jupiter very close. Weather dependent too.

You must be logged in to post a comment.

Image of Rod

Rod

December 9, 2020 at 8:16 pm

Observed 1700-1745 EST. Some good views of the coming conjunction of Saturn and Jupiter tonight using the 90-mm with 40-mm plossl. Saturn and Jupiter slowly getting closer now and easier to see both in the FOV at 25x. Step by step, inch by inch, the pair are getting closer in the eyepiece view :). This promises to be an excellent sight in the telescope, weather permitting. As the pair get closer and closer, I will be able to run up the power while viewing and see better detail on both planets. 21-Dec very close conjunction, about 0.1 degree apart or 6' separation is coming and fast approaching. Tonight, Io and Europa close to Jupiter in the field of view (opposite sides), the other moons farther out. Starry Night simulation view was accurate.

You must be logged in to post a comment.

You must be logged in to post a comment.