Sky at a Glance | December 3rd, 2010

Friday, December 3

  • After dinnertime at this time of year, the M-shaped constellation Cassiopeia floats nearly overhead when you face north (for skywatchers in the world's mid-northern latitudes). Far below Cassiopeia, find Polaris, the North Star. And far below Polaris lies the Big Dipper.

    Jupiter on Nov. 10, 2010
    A new bright white spot (indicated) in the latitude of Jupiter 's South Equatorial Belt was the first sign of events that will probably lead to the whole belt's return. Discoverer Christopher Go took this image at 10:24 UT November 10th. Compare with the later images below. South is up.

  • Jupiter's moon Europa reappears from eclipse out of Jupiter's shadow around 8:34 p.m. EST. A small telescope will show it gradually swelling into view just east of the planet. (For a complete listing of all Jupiter-satellite events this month, good worldwide, see the December Sky & Telescope, page 64.)

    Saturday, December 4

  • Even though it's December, bright Vega, the "Summer Star," remains shining in the northwest in early evening. The brightest star above it is Deneb, the head of the Northern Cross in Cygnus. A little less far to Vega's right is the Lozenge, the head of Draco the Dragon. The Dragon's blunt nose always points to Vega.

    Just above center, the tiny new bright white spot in the latitude of Jupiter 's South Equatorial Belt had already grown a border of dark material by November 12th. Although the white spot doesn't look like much here, its brilliance in methane-band images revealed it to be a violent eruption driving cloud material unusually high into Jupiter's upper atmosphere. Christopher Go took this image at 11:17 UT November 12th, when the System II longitude on Jupiter's central meridian was 292°. South is up.
  • Jupiter's Great Red Spot crosses the planet's central meridian around 8:39 p.m. EST. The central origin of Jupiter's South Equatorial Belt Outbreak transits about 3 hours and 40 minutes later.

    Sunday, December 5

  • Algol is at minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 11:24 p.m. EST (8:24 p.m. PST). Algol takes several additional hours to fade and to rebrighten.

  • New Moon (exact at 12:36 p.m. EST).

    Monday, December 6

  • A twilight challenge! If you live in a narrow zone of the central U.S., Mars will be occulted (covered) by the very thin crescent Moon very low in bright twilight. You'll need optical aid. Map and timetable.

  • Jupiter's Great Red Spot crosses the planet's central meridian around 10:18 p.m. EST.

    Jupiter on Nov. 17, 2010
    November 17th: Three outbreaks now, all in a row! Again, methane-band imagery confirms that the newest, smallest white spot is boiling up to a very high altitude, while the older two seem to be sinking back down. South is up.

    Tuesday, December 7

  • Jupiter's inner moon Io crosses Jupiter's face from 8:35 to 10:49 p.m. Pacific Standard Time. Io's tiny black shadow (more visible) follows behind from 9:55 p.m. to 12:08 a.m. Pacific Standard Time.

  • Today's sunset is the earliest sunset of the year, if you live near 40° north latitude. This is true even though the longest night of the year doesn't come until December 21st (on the solstice). The difference is balanced out by the year's latest sunrise coming on January 4th, a similar distance on the other side of the solstice.

    The mismatch is due to the steady shift at this time of year in the equation of time, caused by the tilt of Earth's axis and (to a lesser extent) the slight ellipticity of Earth's orbit. The effect is revealed graphically on our Skygazer's Almanac that comes with every January's Sky & Telescope. On it, the sunrise and sunset times on every day of the year are symmetrical around the wavy equation-of-time line down its middle, not the straight midnight line.

    Jupiter on Nov. 24, 2010
    By November 24th dark material was spreading far from the outbreak region — and was becoming more detectable visually in amateur telescopes.

    Wednesday, December 8

  • By 7 or 8 p.m. bright Capella is well up in the northeast. To its right in the east is the little Pleiades cluster, with baleful, orange Aldebaran looking on down below it.

  • Algol is at minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 8:13 p.m. EST.

  • Jupiter's Great Red Spot crosses the planet's central meridian around 8:57 p.m. Pacific Daylight Time.

    Thursday, December 9

  • As soon as it gets dark, look for the crescent Moon in the southwest. To the Moon's right, by about three finger-widths at arm's length (depending where you are), is little Alpha Capricorni. If you have sharp vision you can barely see that this is a very close double star. Binoculars resolve it easily.

  • Jupiter's Great Red Spot crosses the planet's central meridian around 7:48 p.m. EST.

  • Have you made plans yet for North America's total eclipse of the Moon on the night of December 20–21? The Moon will be high in the late-night sky. See the December Sky & Telescope, page 61.

    Jupiter on Dec. 1, 2010
    By December 1st the new dark markings had spread more than halfway around the planet as a diagonal ripply band.

    Friday, December 10

  • Bright Jupiter shines far to the upper left of the Moon after dusk. A similar distance to the Moon's right is Altair. Look lower left of the Moon for Fomalhaut, sometimes called "the Autumn Star."

  • Algol is at minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 5:02 p.m. EST. It takes several more hours to rebrighten.

    Saturday, December 11

  • The nearly first-quarter Moon this evening forms a roughly equilateral triangle with bright Jupiter to its upper left and Fomalhaut to its lower left.

  • Jupiter's Great Red Spot crosses the planet's central meridian around 9:27 p.m. EST.



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    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 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 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 must have a detailed, large-scale sky atlas (set of charts). The standards are the
    Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger and deeper Uranometria 2000.0 (stars to magnitude 9.75). And read how to use your charts effectively.

    You'll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the more detailed and descriptive Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.

    Can a computerized telescope take their place? I don't think so — not for beginners, anyway, and especially not on mounts that are less than top-quality mechanically. 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 remains in view low about the southwest horizon during evening twilight. Look about 40 minutes after sunset. Mercury fades from magnitude –0.4 to +0.1 this week.

    Venus blazes in the southeast before and during dawn. It's still at its maximum brightness (magnitude –4.8 or –4.9) and nearly at its maximum height. If fact it's now rising a good two hours before the first glimmer of dawn (for skywatchers at mid-northern latitudes) — a weird UFO of a thing. Look for much fainter Spica to Venus's upper right, and for Saturn a roughly similar distance above Spica.

    Can you follow Venus past sunrise with your unaided eyesight?

    Mars (magnitude +1.3) is basically lost in bright evening twilight. But you can use binoculars to try looking for it to the lower right of brighter Mercury, which is closing in on Mars day by day.

    Jupiter (magnitude –2.5, at the Pisces-Aquarius border) shines in the south to southwest during evening, the brightest starlike point in the sky. In a telescope it's still 42 arcseconds wide. Jupiter's missing South Equatorial Belt is finally re-forming, as dark markings spread east and west around the planet from bright storm spots that broke out in the SEB's latitude a month ago. The original outbreak site transits Jupiter's central meridian about 3 hours and 40 minutes after the Great Red Spot.

    As for the Great Red Spot, it's near System II longitude 157°. Assuming it stays there, here's a list to print out of all the Great Red Spot's predicted transit times for the rest of this observing season.

    Saturn (magnitude +0.9, in Virgo) rises around 2 a.m. and glows in the southeast before and during dawn, about 20° upper right of brilliant Venus. The best time to observe Saturn with a telescope is during early dawn, when the planet will be the least blurred by low-altitude atmospheric turbulence. Saturn's rings have widened to 9° or 10° from edge-on.

    Uranus (magnitude 5.8) is 2½° east of Jupiter.

    Neptune (magnitude 7.9, in Capricornus) is still in the south-southwest right after dark. See our finder charts for Uranus and Neptune online or, with article, in the September Sky & Telescope, page 56.


    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 Daylight Time (EDT) equals Universal Time (also known as UT, UTC, or GMT) minus 4 hours.


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