Sky at a Glance | December 5th, 2008

"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)


Some daily events in the changing sky for December 5 – 13.

Facing southwest in late twilight
Jupiter and Venus are now drawing apart. . . .

Friday, December 5

  • First-quarter Moon (exact at 4:26 p.m. Eastern Standard Time).

  • Mira, the prototype red long-period variable star, is currently visible to the naked eye even through a fair amount of light pollution. On December 3rd it was about magnitude 3.9. Here is its location in Cetus, and here is a closer-up chart with comparison-star magnitudes. Mira is due to reach peak brightness around December 22nd. It seems almost there now.

    Saturday, December 6

  • Although it's just a little thing compared to Venus and Jupiter in the southwest, zero-magnitude Vega is the brightest star high in the west-northwest at the end of twilight. Look higher above it for Deneb. Look farther to Vega's left for Altair. These three stars form the big Summer Triangle.

  • Vesta, the brightest asteroid, is a month past opposition and magnitude 7.1. It's still quite visible with binoculars near the head of Cetus. Use the finder chart in the November Sky & Telescope, page 67, or online.

    Sunday, December 7

  • Earliest sunset of the year (for latitude 40° north). The latest sunrise of the year comes on January 5th, offset from the date of the solstice by an equal amount on the other side.

    Monday, December 8

  • More bright long-period variable stars: Chi Cygni high in the west should peak at 5th magnitude this week; see the comparison-star chart in the December Sky & Telescope, page 68. And R Aquilae in the southwest should still be at or near its 6th-magnitude peak.

    Tuesday, December 9

  • With December well under way, Orion is up in good view in the east-southeast after dinnertime. Tonight you'll find it very far lower left of the Moon. When Orion is rising like this in December, the three stars of Orion's Belt are aligned almost vertically (if you're watching from the mid-northern latitudes). When Orion is on its way to setting, as it does after dark in early spring, Orion's Belt is nearly horizontal.

    Wednesday, December 10

  • The nearly full Moon (97% illuminated) crosses the Pleiades late tonight for skywatchers all across North America. Stars will be occulted on the Moon's invisible dark limb just beyond the bright terminator. The occultations of bright cluster members begin around 2:30 or 3:00 a.m. Thursday morning EST on the East Coast; 10:30 or 11:00 p.m. Wednesday evening PST in the West. Here are local timetables (Universal Times and dates) for the six brightest Pleiads for about 100 cities and towns.

    Looking east soon after dark
    The bright Moon shines among bright constellations in the east these evenings. (These scenes are 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. In the Far East, move it halfway.)

    Thursday, December 11

  • The big bright Moon shines in the east this evening, as shown above. Look to its lower right for Aldebaran, its upper right for the Pleiades, and about twice as far to its left for Capella. Far below the Moon is Orion.

    Facing southwest in twilight
    Getting farther apart. . . .
    Friday, December 12

  • Full Moon (exact at 11:37 a.m. EST). The Moon is just a few hours from its closest perigee of 2008, making this the biggest and brightest full Moon since 1993 — by a slight amount.

    Saturday, December 13

  • The annual Geminid meteor shower should be at its peak tonight, though the moonlight filling the sky will hide many of the meteors. Rates are best from about 10 p.m. until dawn. What with the moonlight, a steady watcher might see one meteor every few minutes on average.

  • Saturn is at western quadrature, 90° west of the Sun in the morning sky.


    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 foldout map in each issue of Sky & Telescope, the essential magazine of 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 it's still less than one per square degree on the sky. Also plotted are many hundreds of good telescopic galaxies, star clusters, and nebulae.
    Sky & Telescope
    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of maps; the standards are
    Sky Atlas 2000.0 or the smaller Pocket Sky Atlas) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion by Strong and Sinnott, the even more detailed Night Sky Observer's Guide by Kepple and Sanner, or the classic Burnham's Celestial Handbook). Read how to use them effectively.

    Can a computerized telescope take their place? 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 and a curious mind." Without these, they note, "the sky never becomes a friendly place."

    More beginners' tips: "How to Start Right in Astronomy".


    This Week's Planet Roundup

    Venus, Jupiter, Moon
    Happy conjunction is happy. On the evening of December 1, 2008, the crescent Moon made an especially good smiley face under eye-like Venus and Jupiter (squint your eyes for a better impression of it) for surprised viewers glancing up in South Asia and Australia. This shot was taken by L. N. Naveen in Bangalore, India.
    Alan MacRobert
    Venus and Jupiter (magnitudes –4.2 and –2.0 respectively), continue pulling apart after their Nov. 30 - Dec. 1 conjunction. They shine in the southwest during twilight. Jupiter is moving off to Venus's lower right.

    In a telescope Venus is still small (17 arcseconds wide) and gibbous (67% illuminated). Jupiter is 34″ or 33″ wide but has a much lower surface brightness; being 7 times farther from the Sun, Jupiter is lit only about 1/49 as brightly.

    Mercury and remain hidden in the glare of the Sun.

    Saturn (magnitude +1.1, near the hind foot of Leo) rises around midnight and shines high in the south by dawn. Don't confuse Saturn with similarly-bright Regulus 21° (about two fist-widths at arm's length) to its upper right after they rise, and directly to its right at dawn.

    A telescope will show that Saturn's rings have closed to only 1° from edge on! They'll reach a minimum of 0.8° at the end of December, then start opening again, before finally closing to exactly edge-on next September — when Saturn will, unfortunately, be in conjunction with the Sun.

    Sad conjunction is sad. Hours later, by the time of twilight in North America on December 1st, the crescent Moon had moved over to the other side of Venus and Jupiter, creating a frowny face. (Tilt your head around to see it.) Sky & Telescope's Sean Walker took this shot from New Hampshire. In the time between, the Moon crossed right over Venus for western Europe. See our photo gallery.
    S&T: Sean Walker
    Uranus and Neptune (magnitudes 5.8 and 7.9, respectively, in Aquarius and Capricornus) are in the southwest and south right after dark. Uranus is 0.1° from the similarly-bright star 96 Aquarii. Use our article and finder charts or the chart in the September Sky & Telescope, page 63.

    Pluto is hidden in the glare of the Sun.

    All descriptions that relate to your horizon or zenith — 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 (known as UT, UTC, or GMT) minus 5 hours.


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