This Week’s Sky at a Glance, December 19 – 27

Some daily sky sights among the ever-changing Moon, planets, and stars.

Friday, December 19

Have you ever tried to catch Sirius actually rising? If you can find a good view down to the east-southeast horizon, watch for Sirius emerging about two fists at arm's length below Orion's Belt. It now rises sometime around 7:30 or 8 p.m. local time, depending on your location. When a star is very low, it tends to twinkle quite slowly and often in vivid colors. Sirius is bright enough to show these effects well.

Moon and Saturn at dawn, Dec. 20, 2014

The waning Moon on the morning of Saturday the 20th is only a day and a half from new. This is the view about 45 minutes before sunrise (exact for the middle of North America).

In early dawn Saturday morning, see if you can spot Saturn and the waning Moon low in the southeast, as shown here. The best time is probably about 60 minutes before sunrise, depending on clouds and atmosphere.

Saturday, December 20

You are remembered, Carl Sagan (November 9, 1934 – December 20, 1996).

Two deep mutual eclipses happen among Jupiter's moons! Callisto will cast its shadow onto Io from 10:13 to 10:32 p.m. Eastern Standard Time, then it will do so again from from 6:49 to 7:12 a.m. Sunday morning EST (3:49 to 4:12 a.m. Sunday morning PST). At mid-eclipse in both cases, Io should dim by a very noticeable 1.1 magnitude. Compare it carefully with the brightnesseses of Jupiter's other moons.

For the first of these eclipses, Io will appear just to Jupiter's east quite close to Ganymede, which is normally only 0.4 magnitude brighter. Dimmer Callisto will be farther east. The timing is excellent for observers in Europe, though you'll have to go out very late; add 5 hours to the times above to get UT. The timing is fair for North America's East Coast, where Jupiter will be rather low in the east. Westerners miss this one.

For the second eclipse, Jupiter will be high in the dark for the western half of North America. Callisto, Io, and Ganymede will be more evenly spaced east of Jupiter, with Io in the middle.

Sunday, December 21

The solstice occurs at 6:03 p.m. EST, when the Sun reaches its farthest point south for the year and begins its six-month return northward. This is the longest night and the start of winter in the Northern Hemisphere; the longest day and the start of summer in the Southern Hemisphere. Happy Yule!

New Moon (exact at 8:36 p.m. EST).

Monday, December 22

Shortly after sunset, look for the hairline crescent Moon to the right of Venus (from North America). This is a challenging observation; bring binoculars.

Moon, Mars and Venus at dusk, Dec. 23-25, 2014

Back in the evening sky, the Moon now waxes past Venus and Mars.

Tuesday, December 23

Now the crescent Moon is much easier to see in twilight. Spot Venus below it, as shown here.

Maybe you're familiar with the ET Cluster, NGC 457 in Cassiopeia. But what about its neighbor Sharpless 2-173, a faint nebula containing the weak cluster Mayer 1? Use the Queen's Kite asterism to get there, as Sue French shows in her Deep-Sky Wonders chart and column in the December Sky & Telescope, page 56.

Wednesday, December 24

Tiny Mars in twilight glimmers to the left of the increasingly thick crescent Moon, as shown here.

Thursday, December 25

Now Mars is far below the Moon at dusk.

Got a first telescope for Christmas? Know someone who did? Some advice: What to See with Your New Telescope.

Friday, December 26

This is the time of year when Orion shines in the east-southeast after dinnertime. He's well up now, but his three-star Belt is still nearly vertical. The Belt points up toward Aldebaran and, even higher, the Pleiades. In the other direction, it points down to where bright Sirius is about to rise.

Saturday, December 27

The Moon is almost first-quarter this evening. Look to its upper right after dinnertime for the Great Square of Pegasus again balancing on one corner.


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. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

Pocket Sky Atlas

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's still less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and once you know your way around, the even larger 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, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

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 (able to point with better than 0.2° repeatability, which means fairly heavy and expensive). 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 is buried in the sunset.

Venus (magnitude –3.9) is beginning to show through the glow of sunset. Look for it just above the southwest horizon 20 or 30 minutes after sundown. The farther south you live, the higher it will appear.

Mars (magnitude +1.1, in central Capricornus) still glows in the southwest during and after twilight. And it still sets around 8 p.m.

Jupiter (magnitude –2.4, in western Leo) rises in the east-northeast around 9 p.m. About 45 minutes later, fainter Regulus (magnitude +1.4) rises below it. By dawn they shine in the west-southwest — with Regulus now to Jupiter's upper left.

Saturn (magnitude +0.5, between Libra and Scorpius) glows fairly low in the southeast before and during dawn. Look for it far below Arcturus. Late in the week, use binoculars to start looking for Antares twinkling way under Saturn as dawn grows bright.

Uranus (magnitude 5.8, in Pisces) and Neptune (magnitude 7.9, in Aquarius) are in the south and southwest, respectively, right after dark. Use binoculars or a small telescope and our finder charts for Uranus and Neptune.

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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, or GMT) minus 5 hours.


"Imagination will often carry us to worlds that never were. But without it we go nowhere."

— Carl Sagan


One thought on “This Week’s Sky at a Glance, December 19 – 27

  1. mary bethmary beth

    Beautiful, cold, starry Christmas Eve here in Houston, Tx. I finally got to see bright Venus in the orange glow of the sunset. Spectacular! I think i saw Santa flying near Orion! Merry Christmas to all and to all, a clear night!

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