Sky at a Glance | December 13th, 2013

Friday, December 13

  • The Geminid meteor shower should be at its peak tonight, from 9 or 10 p.m. until dawn Saturday morning. The best viewing time is actually after your local moonset: in the hour before the beginning of morning twilight Saturday. But bright meteors will show even through the moonlight earlier. See our article, Geminid Meteors to Pierce the Moonlight.

  • The eclipsing binary star Algol should be at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 9:50 p.m. EST Friday evening.

    The Moon brightens as it waxes to become full on the night of the 16th. (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.)

    Saturday, December 14

  • The bright gibbous Moon shines in Taurus this evening. Through the glare, can you make out the Pleiades roughly a fist-width to its upper left? Easier is Aldebaran farther to the Moon's lower left. Brighter Capella shines much farther left of the Moon.

    Sunday, December 15

  • This evening look for Aldebaran just 2° to 4° lower right of the bright Moon (for North America), as shown at right. Although they look close together, Aldebaran is 1.5 billion times farther away.

    Monday, December 16

  • Full Moon tonight (exact at 4:28 a.m. Tuesday morning EST). As the Moon climbs the eastern sky this evening, look for Aldebaran to its upper right, Aldebaran-colored Betelgeuse to its lower right, Capella farther to its upper left, and Jupiter far to its lower left.

    Tuesday, December 17

  • The bright Moon shines in the dim Club of Orion this evening (for the Americas). No, the Moon doesn't always stay quite within the constellations of the zodiac. Lower left of the Moon is Jupiter, and lower right of it is Betelgeuse.

    Wednesday, December 18

  • The Moon and Jupiter shine together after they rise in early evening, with Pollux and Castor to their left. Although Jupiter looks close to the Moon, it's 1,600 times farther away.

    Thursday, December 19

  • Once the waning gibbous Moon rises after dinnertime, you'll find Jupiter above it, Pollux and Castor left of Jupiter, and Procyon to the Moon's right or lower right. Much farther right of Procyon, watch for brilliant Sirius coming up.

    Friday, December 20

  • This evening, use a telescope to watch Io disappear into eclipse by the shadow of Jupiter around 9:15 p.m. Eastern Standard Time, barely off Jupiter's western limb. Forty-five minutes later, Ganymede emerges onto dark sky in front of Jupiter's western limb. Then around 11:23 p.m. EST, the Great Red Spot (strong orange this season) transits Jupiter's central meridian.

    To keep up with any and all such events this month worldwide, see "Action at Jupiter" in the December Sky & Telescope, pages 51 and 52.

    Saturday, December 21

  • Today is the shortest day of the year in the Northern Hemisphere, and the longest day in the Southern Hemisphere. Winter in the north begins at the solstice: at 12:11 p.m. Eastern Standard Time. Happy Yule.

  • If there'e one constellation that everyone should know at this time of year, it's wintry Orion climbing up in the east-southeast. As always when Orion is on the rise, the three-star Belt of Orion in its middle is nearly vertical. Show someone Orion this week and they'll know it for a lifetime.


    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 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 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 heavy and expensive). 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. 11, 2013
    Jupiter on December 11th, imaged almost as well as it ever can be from Earth. Christopher Go used a Celestron-14 scope from his apartment balcony in Cebu City, Philippines. South here is up. Just visible on the right end of the Great Red Spot is Europa, nearly white. More obvious is Europa's black shadow. It's being cast toward celestial west ("preceding") because Jupiter has not yet reached opposition.


    The System II longitude at the time of this image was 199°. Through the eyepiece of a medium-aperture scope when Jupiter is again turned this way, in moments of good seeing you should be able to see the Red Spot's unusually strong orange color, the turbulence on its following (celestial east) side, perhaps the white ovals south of it, the differing widths and darknesses of the big South and North Equatorial Belts, and perhaps the blue festoons in the Equatorial Zone.


    Mercury is lost in the glare of the rising Sun.

    Venus (magnitude –4.9) is the brilliant "Evening Star" in the southwest during and after dusk. It's moving lower now day by day as it wanes to a thinner crescent: from 21% sunlit on December 13th to 14% lit on the 20th. During this time, the crescent enlarges from 41 to 51 arcseconds from horn to horn.

    Mars (magnitude 1.1, in the head of Virgo) rises around midnight or 1 a.m. By dawn it's very high in the south, but in a telescope Mars is still very small and gibbous: only 6 arcseconds in diameter. Mars passes 3/4° north of the 3.5-magnitude star Eta Virginis on the 17th and 18th.

    Jupiter (magnitude –2.7, in Gemini) rises in the east-northeast around the end of twilight, with Pollux and Castor to its left. It blazes highest around 1 or 2 a.m. In a telescope Jupiter has grown to a big 46 arcseconds wide as it nears its January 5th opposition. See lots about observing Jupiter in the January 2014 Sky & Telescope.

    Saturn (magnitude +0.6, in Libra) is in the southeast as dawn begins to brighten. Look for it far to the lower left of Mars and Spica, and far lower right of brighter Arcturus.

    Uranus (magnitude 5.8, in Pisces) and Neptune (magnitude 7.9, in Aquarius) are still well placed right after dark in the south and southwest, respectively. 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) is Universal Time (UT, UTC, or GMT) minus 5 hours.


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