This Week’s Sky at a Glance, December 8 – 16

Mother of all Geminids makes a near-Earth pass. The asteroid 3200 Phaethon, source of the Geminid meteoroid stream, should reach about 11th magnitude from December 12th through 17th as it passes several million miles from Earth. That's bright enough for medium-size telescopes. It'll be perfectly placed high in the evening sky. See our article and finder charts.

Moon and Regulus at dawn, Dec. 9, 2017

The Moon, almost last quarter, stands high under Leo as dawn begins to brighten Saturday morning the 9th.

Friday, December 8

• Bright Vega still shines well up in the west-northwest after dark at this time of year. The brightest star above it is Deneb, the head of the big Northern Cross, which is formed by the brightest stars of Cygnus. At nightfall the shaft of the cross extends lower left from Deneb. By about 11 p.m., the cross plants itself more or less upright on the northwest horizon.

Saturday, December 9

• The W pattern of Cassiopeia stands on end in early evening, very high in the northeast. The bottom star of the W is Epsilon (ε) Cassiopeiae. That's your starting point for hunting down the little-known star cluster Collinder 463, sparse and loose but visible in binoculars. It's 8° to Epsilon's north (the direction toward Polaris), and is surrounded by a nice quadrilateral of 4th- and 5th-magnitude stars about 3° wide. Use Chart 1 of the Pocket Sky Atlas — or Matt Wedel's Binocular Highlights column in the December Sky & Telescope, page 43.

• Last-quarter Moon (exact at 2:51 a.m. on the 10th Eastern Standard Time). The Moon rises around 11 or midnight tonight, in the head of Virgo below Leo.

Sunday, December 10

• 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 is standing straight up on its handle in fine view in the northeast.

Monday, December 11

• Orion is coming into good view low in the east after dinnertime now. And that means Gemini is also coming up 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 constellation — one over the other, with Castor on top.

• Noticing any early Geminid meteors yet? See Wednesday below!

Moon, Mars and Jupiter at dawn, Dec. 13-16, 2017

Watch the waning Moon march down past Mars and Jupiter these mornings. Alpha (α) Librae is a nice, very wide double star for binoculars.

Tuesday, December 12

• In the dawn of Wednesday the 13th, the thin waning crescent Moon hangs above little Mars in the southeast, as shown at right. Spica, a bit brighter, shines farther to the Moon's left (out of the frame). Farther lower left of the Moon, you'll find much brighter Jupiter.

Wednesday, December 13

• The Geminid meteor shower should be at its peak late tonight, and there's no Moon to interfere. Bundle up warmly. Bring a reclining lawn chair to a dark spot with no glary lights and an open view of the sky. Lie back, gaze into the stars, and be patient. Under a dark sky you might see a meteor at least once a minute on average. Light pollution cuts down on the numbers. See our article Fantastic Year for Geminid Meteor Shower.

You'll see the most meteors from about 10 p.m. until dawn local time, when your side of Earth turns to face most directly into the oncoming meteoroid stream. But any that you may see early in the evening, when the shower's radiant in Gemini is still low, will be long, dramatic "Earth-grazers" skimming into the upper atmosphere at a shallow angle.

• In the early dawn of Thursday the 14th, Jupiter shines below or lower right of the thin waning crescent Moon, as shown here. A nice sign-off for an early-morning Geminid watch!

Thursday, December 14

• The five brightest stars of Cassiopeia are usually called a W. At nightfall the W stands on end very high in the northeast, but by mid-evening it turns over to become a flattened M even higher in the north. Explore Cassiopeia's leading telescopic jewels (there are many!) with Sue French's Deep-Sky Wonders article, chart, and photos in the December Sky & Telescope, page 55.

• As dawn begins to brighten on the morning of Friday the 15th, look low in the southeast for the thinning crescent Moon. It forms the end of a ragged diagonal line with Jupiter, Mars, and Spica extending to its upper right.

And a small telescope will show Jupiter's moons Ganymede, Callisto, and Europa bunched in a tight little triangle off the planet's western (upper right) side.

Friday, December 15

• As the Summer Triangle sinks lower in the west, Altair is the first of its stars to go. Start by spotting bright Vega 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 it in view?

Saturday, December 16

• Have you ever watched a Sirius-rise? Find an open view right down to the east-southeast horizon, and watch for Sirius to come up about two fists at arm's length below Orion's vertical Belt. Sirius comes up sometime around 8 p.m. now, 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, especially with binoculars.


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.

Pocket Sky Atlas, 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 above is the Jumbo Edition for easier reading in the night. Larger view. Sample chart.

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, is 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, 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 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, Venus, and Saturn are hidden in the glare of the Sun.

Mars and Jupiter (magnitudes +1.6, and –1.7, respectively) rise in the east-southeast around 3 a.m. and 4 a.m., respectively. First up is Mars. Spica sparkles to its upper right, a little farther from it every day. Then bright Jupiter rises to Mars's lower left. By early dawn, they're both well up in the southeast. Mars is in Virgo; Jupiter is in Libra.

Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.9, in Aquarius) are well placed in the southeast and south, respectively, right after dark. Use our finder charts online or in the October Sky & Telescope, page 50.


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 (also called UT, UTC, GMT, or Z time) minus 5 hours.


"Science is built up of facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house."
— Henri Poincaré (1854–1912)


"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


"Objective reality exists. Facts are often determinable. Vaccines save lives. Carbon dioxide warms the globe. Bacteria evolve to thwart antibiotics, because evolution. Science and reason are not fake news, not a political conspiracy. Civilization's survival depends on our ability, and willingness, to use them."
— Alan MacRobert, your Sky at a Glance editor


"Facts are stubborn things."
— John Adams, 1770


One thought on “This Week’s Sky at a Glance, December 8 – 16

  1. TaurusTaurus

    Have you reduced your Sky at a Glance RSS feed to just show the summary? My feed reader has been showing the summary only for the last few articles! I hope it’s not so.

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