This Week's Sky at a Glance, December 1 – 9

FRIDAY, DECEMBER 1

■ Two faint fuzzies naked-eye: The Andromeda Galaxy (M31) and the Perseus Double Cluster are two of the most famous deep-sky objects. They're both cataloged as 4th magnitude, and in a fairly dark sky you can detect each with the unaided eye. Binoculars make them easier. They're located only 22° apart, very high toward the east early these evenings — to the right of Cassiopeia and closer below Cassiopeia, respectively.

But they look rather different, the more so the darker your sky. See for yourself. You can find them by carefully using the all-sky constellation map in the center of the December Sky & Telescope.

■ In early dawn Saturday morning December 2nd, look for Spica 5° to the right of brilliant Venus as shown below. Venus is currently 8 light-minutes away. Spica is out there at 250 light-years; it's a blue giant, spectral type B0, a very close ellipsoidal binary pair putting out 23,000 times the light of the Sun.

SATURDAY, DECEMBER 2

■ The Summer Triangle is still pretty high right after dark. Vega, its brightest star, shines in the west-southwest. Deneb is about two fists above it. Altair is farther to Vega's left.

Above Altair by hardly more than a fist is little Delphinus, the Dolphin. Closer to Altair's upper right is smaller, fainter Sagitta, the Arrow. Binoculars help! Both constellations are about 5° long, so they will just fit into the field of view of most binoculars.

■ Polaris is, as always, due north. This is the time of year when the Little Dipper extends lower left from it in early evening. The only moderately bright stars of the Little Dipper are Polaris and Kochab, the star marking the lip of its bowl. Both are 2nd magnitude. They're 17° apart. How much of the rest of the faint Little Dipper can you make out between them, if any, given the quality of your sky?

By about 11 p.m. Kochab has swung to be straight under Polaris.

SUNDAY, DECEMBER 3

■ The waning Moon, nearly last quarter, rises around 10 or 11 p.m. in the east-southeast. As it gains height, catch an early sighting of Regulus, usually thought of as a star of late winter and spring, 3° or 4° to the Moon's right.

Regulus is the brightest star of the Sickle of Leo. The Sickle extends upper left from Regulus (the bottom of the its handle) by a fist at arm's length or a little more.

MONDAY, DECEMBER 4

■ Last-quarter Moon tonight (exact at 12:49 a.m. EST). The Moon rises around 11 or midnight local time and is now more than a fist at arm's length below Leo's Sickle. By the time Tuesday's dawn begins to break the Moon is high in the south, and the Sickle stands upright to the Moon's upper right.

TUESDAY, DECEMBER 5

■ At this time of year the Big Dipper lies down lowest soon after dark, due north. If you're as far south as Miami, it's entirely below the north horizon.

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 stand nearly upright on the bright end of its W shape.

WEDNESDAY, DECEMBER 6

■ Jupiter's moon Io crosses onto Jupiter's face at 6:47 p.m. EST, moving from celestial east to west, followed by its tiny black shadow at 7:36 p.m. EST. They depart Jupiter's western limb at 8:56 and 9:46 p.m. EST, respectively. Meanwhile, Jupiter's Great Red Spot crosses the planet's central meridian around 9:26 p.m. EST.

THURSDAY, DECEMBER 7

■ Earliest sunset of the year (if you're near latitude 40° north). By the time of the solstice and longest night on December 21st, the Sun actually sets 3 minutes later than in does now. And the latest sunrise doesn't come until January 5th. These slight discrepancies arise from the tilt of Earth's axis and the ellipticity of Earth's orbit.

■ The Pleiades and Aldebaran below them are well up in the east after dark. So you know Orion can't be far behind below them. Orion's whole main figure, formed by his seven brightest stars, takes about 1 hour 20 minutes to clear the horizon. By 8 or 9 p.m. Orion is up in fine view.

■ Before and during early dawn Friday morning the 8th, look southeast for the waning crescent Moon. Spot Spica, magnitude +1.0, a couple degrees below it, as shown here, before the sky gets too bright.

FRIDAY, DECEMBER 8

■ M31, the Andromeda Galaxy, passes your zenith sometime around 7 or 8 p.m. if you live in the world's mid-northern latitudes. The exact time depends on how far east or west you live in your time zone. Binoculars will reveal the dim little glow of 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.

■ Before and during dawn Saturday morning the 9th, catch the lovely meetup in the eastern sky of Venus and the thin crescent Moon: Astarte and Diana, respectively, for the classically minded. They're about 4° apart.

SATURDAY, DECEMBER 9

■ Orion is coming into good view low in the east-southeast 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 Gemini constellation — one over the other, with fainter Castor on top.

SUNDAY, 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 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, curved and narrow. Its brightest stars are only 8th and 9th magnitude, so use averted vision. Find your way using Chart 1 of the Pocket Sky Atlas.

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This Week's Planet Roundup

Mercury, fading from magnitude –0.4 to –0.2 this week, settles down even lower into the sunset afterglow. Early in the week, try looking for it just above the southwest horizon about 30 or 40 minutes after sunset. Bring binoculars. The farther south you are, the less low it will be.

Venus, magnitude –4.2, shines as the bright "Morning Star" in the southeast before and during dawn. It rises above the east horizon about 2 hours before dawn's first light. Watch for it to come up about three fists at arm's length lower right of Arcturus, the brightest star twinkling in the east.

Mars is out of sight behind the glare of the Sun.

Jupiter (magnitude –2.8, in Aries) is that bright white dot dominating the high east to southeast in early evening. It stands highest in the south around 9 p.m.

Saturn (magnitude +0.9, in dim Aquarius) glows yellowish high in the south-southwest just after dark. Fomalhaut, similarly bright, twinkles almost two fists at arm's length to Saturn's lower left. Saturn declines toward the southwest as evening progresses and sets by about 10 p.m. So get your telescope on it early!

Uranus, magnitude 5.6 in Aries, awaits your binoculars in the darkness 14° east of Jupiter. In a telescope at high power Uranus is a tiny but distinctly nonstellar ball, 3.8 arcseconds in diameter. Locate and identify it using the finder charts in the November Sky & Telescope, pages 48-49.

Neptune, fainter at magnitude 7.9, is at the Aquarius-Pisces border 23° east of Saturn, making it high in the early-evening dark. Neptune is only 2.3 arcseconds wide: harder to resolve as a ball than Uranus, but definitely nonstellar at high power.

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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 and graphics that also depend on longitude (mainly Moon positions) are for North America.

Eastern Standard Time (EST) is Universal Time minus 5 hours. UT is also known as UTC, GMT, or Z time.

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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 a more detailed 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 much more 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 all 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 mag 9.75). And read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet as to charts on paper.

You'll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham's Celestial Handbook. An impressive more modern one is the big Night Sky Observer's Guide set (2+ volumes) by Kepple and Sanner.

Can computerized telescopes replace charts? Not for beginners I don't think, especially not on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting finicky technology to work rather than learning the sky. 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."

But finding a faint telescopic object the old-fashioned way with charts isn't simple either. Learn the tricks at How to Use a Star Chart with a Telescope. 

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Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the naked-eye heavens above. It's free.

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"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

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