Mercury and Saturn in the sunset, Dec. 1, 2017
On Friday December 1st, Mercury and Saturn are 3° apart very low after sunset. Their visibility in bright twilight is exaggerated here. (The blue 10° scale is about the width of your fist held at arm's length.)
Mars, Spica, Jupiter, Venus in the dawn of Dec. 2, 2017
Mars and Spica look down at Jupiter in the dawn. And, can you get a last glimpse of Venus barely above the pre-sunrise horizon?

Friday, December 1

• Can you still catch Saturn and Mercury deep in the bright afterglow of sunset, as shown at right? Bring binoculars!

• The waxing gibbous Moon shines in the east this evening. Look upper right of it for the two brightest stars of Aries, left of it for the little Pleiades cluster, and below the Pleiades for orange Aldebaran.

Saturday, December 2

• The nearly-full Moon shines in Taurus this evening, upper right of Aldebaran and below or lower right of the Pleiades.

Does the Moon look just a trace bigger than usual? You're right! Tomorrow's full Moon is a "supermoon."

Telescope users from the extreme Pacific Northwest through Alaska can see the Moon occult Aldebaran on Sunday morning the 3rd (map and timetables).

• Now that the Pleiades and Aldebaran are up due east, can Orion be far behind? Orion's entire iconic figure, formed by its brightest seven stars, takes about an hour and a quarter to cross the horizon below Aldebaran. By 10 p.m. Orion is well up in fine pre-winter view, under the Moon.

Sunday, December 3

• Full Moon (exactly full at 10:47 a.m. EST). This is a "supermoon"; the Moon is near perigee. In fact this is the closest full Moon of 2017. But the difference from average is slight. Can you really detect that this full Moon is a little larger than usual? With enough careful practice moonwatching, yes you can.

The Moon is in Taurus, with orange Aldebaran now to its upper right in the evening. The Pleiades are above Aldebaran. Orange Betelgeuse rises below the Moon not long after dark.

Monday, December 4

• Once the Moon is well up in the east, look to its right or lower right for Betelgeuse. The rest of Orion extends farther right or lower right.

Tuesday, December 5

• Now the waning gibbous Moon doesn't rise until well after dark. Look for Pollux to its left, and Castor above Pollux. Later into the night, you'll find Procyon rising farther to the Moon's lower right.

Wednesday, December 6

• The five brightest stars of Cassiopeia are usually called a W, but late these nights Cas turns over to become a wide M, very high in the north.

• The late-evening waning Moon shines below Pollux and Castor and left of Procyon.

Thursday, December 7

• Earliest sunset of the year (if you're near latitude 40° north). By the time of the solstice and shortest day on December 21st, the Sun actually sets 3 minutes later than now. But the Sun doesn't rise its latest until January 4th. For these slight discrepancies, blame the tilt of Earth's axis and the ellipticity of Earth's orbit.

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 toward 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.)


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 and Saturn are disappearing deep down in the afterglow of sunset.

Venus is getting lost very deep in the glare of sunrise.

Mars and Jupiter (magnitudes +1.7, and –1.7, respectively) rise well before dawn in the east-southeast. First up is Mars, accompanied by Spica to its right or upper right. Bright Jupiter rises about an hour after Mars, still well before dawn begins.

Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.9, in Aquarius) are well placed in the southeast and south, respectively, in early evening. 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



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