Friday, December 7

  • This is the time of year when the Andromeda Galaxy, M31, passes the zenith in early evening for skywatchers at mid-northern latitudes. It goes exactly through your zenith if you're at 41° north latitude (New York, Denver). When this happens depends on your location.

    The two brightest asteroids are looping near Jupiter. Click the image for our detailed finder chart, big and printable for use outdoors.

    Tony Flanders


    Saturday, December 8

  • Since Jupiter is just past opposition, the asteroids Ceres and Vesta in Jupiter's vicinity are near their oppositions too. Vesta's opposition is tonight. It's magnitude 6.4, and Ceres is 6.9. Spot them in binoculars this month using our finder chart in the December Sky & Telescope, page 50, or online. They're near the horns of Taurus.
  • Algol in Perseus, the prototype eclipsing binary star, should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 12:29 a.m. Sunday morning EST; 9:29 p.m. Saturday evening PST. Algol takes several additional hours to fade and to rebrighten.
  • Jupiter's moon Io reappears out of eclipse from Jupiter's shadow at 11:49 p.m. EST; 8:49 p.m. PST.

    For all of Jupiter's satellite events, as well as all of the Great Red Spot's transit times, get our handy new JupiterMoons app!

    Dawn view

    At dawn, watch the waning crescent Moon step down past Spica, Saturn, Venus and Mercury from one morning to the next. As always, this scene is drawn for the middle of North America. European observers: move each Moon symbol a quarter of the way toward the one for the previous date. For clarity, the Moon is shown three times actual size.

    Sky & Telescope diagram

  • During dawn Sunday morning the waning crescent Moon hangs close to Spica, as shown at right.

    Sunday, December 9

  • Jupiter's Great Red Spot should transit the planet's central meridian around 9:15 p.m. EST.
  • At dawn Monday morning, look upper left of the Moon for Saturn, and lower left of the Moon for little Alpha Librae partway down to Venus and Mercury, as shown at right. If you catch Alpha Lib before dawn becomes too bright, binoculars will show it to be a wide double star.

    Monday, December 10

  • Low in the southeast in early dawn Tuesday morning, the waning crescent Moon is beautifully paired with Venus, as shown at right.

    Tuesday, December 11

  • Flyby of Toutatis. The small Earth-crossing asteroid 4179 Toutatis is performing one of its close approaches to Earth tonight, as it does every four years. Locate it creeping across the stars of Cetus and Pisces using at least a 3- or 4-inch telescope tonight through Friday night. It's magnitude 10.9 tonight and peaks at 10.5 on Friday. Use the finder charts for each of these four nights in the December Sky & Telescope, page 53, or online.
  • Algol should be at its minimum light for a couple hours centered on 9:18 p.m. EST. Here's a comparison-star chart giving the magnitudes of three stars near Algol; use them to judge its changing brightness.

    Wednesday, December 12

  • As the stars come out in late twilight, the flattened W of Cassiopeia is still standing on one end high in the northeast. By as early as 8 p.m. it turns around to be a horizontal M, even higher in the north.

    Facing high southwest at 2 a.m.

    The path of any Geminid meteor you see will, if traced far enough back across the sky, cross a spot near the heads of Gemini. This very wide-field scene (from horizon to zenith) is for about 2 a.m. as seen from mid-northern latitudes.

    Sky & Telescope diagram


    Thursday, December 13

  • The Geminid meteor shower, often the best in the annual meteor calendar, should be at its maximum late tonight. And there's no Moon. See our article, Geminid Meteors to Peak the Night of Dec. 13th.
  • New Moon (exact at 3:42 a.m. on the 13th EST).

    Friday, December 14

  • Orion stands centered between two bright lights this year. High above it during evening shines bright Jupiter (with its orange sidekick Aldebaran). A similar distance below Jupiter, Sirius rises around 8 p.m. (the time depends on your location) — with its white sidekick Mirzam.

    Sirius, just 8.6 light-years away, is the brightest star in the night sky. It's also the closest that's ever visible to the unaided eye from mid-northern latitudes.

  • Algol should be at minimum light for a couple hours centered on 6:07 p.m. EST. Watch it rebrighten for much of the rest of the night.
  • Jupiter's Great Red Spot should cross Jupiter's central meridian around 8:22 p.m. EST. For all of the Great Red Spot's transit times, as well as all of Jupiter's satellite events, get our handy new JupiterMoons app.

    Saturday, December 15

  • In early evening, the "Summer Star" Vega is still the brightest thing in the northwestern sky, though it's moving ever lower. The brightest above it is Deneb. Vega is 25 light-years away; supergiant Deneb is about 1,400.

    Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

    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 that's less than one star in an entire telescopic field of view, on average. By comparison, Sky Atlas 2000.0 plots 81,312 stars to magnitude 8.5, typically one or two stars per telescopic field. Both atlases include many hundreds of deep-sky targets — galaxies, star clusters, and nebulae — to hunt among the stars.

    Sky & Telescope


    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 the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope effectively.

    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 certainly not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable 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

    Jupiter on Dec. 10, 2012

    Christopher Go again shows what is possible imaging Jupiter with a 14-inch scope, a high-end planetary video camera, excellent seeing — and a whole lot of skill from years of practice. Don't expect to see anything approaching this visually in any telescope, or to get results like this on your first tries imaging.

    South here is up. Upper left of the Great Red Spot is Oval BA ("Red Spot Junior") closely followed by a tiny dark red dot. Just upper right of the Great Red Spot is Europa, barely visible against Jupiter's clouds, followed by its black shadow on the clouds. Following behind the Great Red Spot itself is a huge area of white turbulence roiling the South Equatorial Belt.

    The South Temperate Belt is barely visible along some of its length but prominent on the following side of the Great Red Spot. On the north side of the planet, the North Equatorial and North Temperate belts have become cleanly separated by the North Tropical Zone's return to whiteness.

    Christopher Go


    Mercury, Venus, and Saturn form a diagonal line in the southeast as dawn begins to brighten. Venus is by far the brightest, at magnitude –3.9. Look well to its upper right for Saturn, magnitude +0.7, and farther on for Spica, magnitude +1.0. Look lower left of Venus for Mercury, magnitude –0.5. Mercury is having its best morning apparition of 2012. This line of four points is lengthening: it grows from 33° to 42° long this week.

    And watch the waning crescent Moon step down the line on the mornings of December 9, 10, and 11, as shown above.

    Mars (magnitude +1.2, in Sagittarius) remains low in the southwest in evening twilight. In a telescope it's just a tiny blob 4.3 arcseconds in diameter — hardly larger than Uranus!

    Jupiter (magnitude –2.8, in Taurus) is just past opposition. As twilight fades it's already glaring low in the east. It climbs to dominate the eastern and southeastern sky through the evening, with orange Aldebaran 5° to its lower right and the Pleiades about twice as far to its upper right. Jupiter is highest in the south around 11 or midnight. In a telescope it's a big 48 arcseconds wide, essentially as large as it ever appears.

    Uranus (magnitude 5.8, in Pisces) and Neptune (7.9, in Aquarius) are conveniently placed in the south right after dusk but move lower later. 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) equals Universal Time (also known as UT, UTC, or GMT) minus 5 hours.

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    • About Alan MacRobert

    Alan M. MacRobert became an avid Sky & Telescope subscriber in 1966 at age 14, joined the editorial staff in 1982, and is now a senior contributing editor, semi-retired. He played a role in practically every part of the magazine and the company's other products for more than a generation, both on the amateur-observing side and the science-reporting side. In 1994 a book collection of his observing how-tos and telescopic sky tours was published as Star Hopping for Backyard Astronomers. He has produced This Week's Sky at a Glance online every week since 1989.

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