Sky at a Glance | December 14th, 2007

Some daily events in the changing sky for December 14 – 22.

No matter how faint it gets or bright it stays, Comet Holmes will remain in Perseus all the way into next March. (The comet symbols are plotted at 0:00 Universal Time on the dates indicated. This is on the evening of the previous date in the time zones of the Americas. Click chart for larger version.)
Sky & Telescope
Comet Holmes remains high in Perseus, dim but big. Look for it southwest of Alpha Persei. You may need binoculars now that moonlight is returning to the evening sky — or go out and look after the Moon sets. (To find your local moonset time use our online almanac. Make sure the Daylight Saving Time box is unchecked.)

Give your eyes plenty of time to dark-adapt. Although the comet's total brightness has remained remarkably constant for weeks (light curve; scroll down), its widening size means that its surface brightness is decreasing. And this makes it tougher to see through any moonlight or light pollution. See our ongoing article.

Also, another comet is on the way in! Comet 8P/Tuttle is magnitude 8 and brightening more or less on schedule. It should reach 6th magnitude from late December through mid-January. And while Comet Holmes stays stuck in Perseus for months, Comet Tuttle (being much nearer) will move far southward across the evening sky during the same time. See the article and charts in the January Sky & Telescope, page 73, and the brief version online.

During the 2004 Geminid meteor shower, Alan Dyer caught a bright fireball with a tripod-mounted digital camera. He used a wide-field, 16-mm lens for a 1-minute exposure at f/2.8 with an ISO setting of 800. Expect to shoot a lot of frames before you get this lucky. Click image for larger view.
Alan Dyer
Friday, December 14

  • The Geminid meteor shower should still be active tonight. From late evening until dawn, you might see a meteor every minute or two on average if you have excellent sky conditions. See our short article online and the full version in the December Sky & Telescope, page 71.

    Saturday, December 15

  • It's not even winter yet, but already the Big Dipper is beginning its long annual rise in the evening sky, coming up bowl-first. By 9 p.m., look for it creeping up through the bare tree branches in the north-northeast. The Dipper will float highest overhead on the warm evenings of May and June.

    Sunday, December 16

  • Whenever the Big Dipper is starting its rise, the Little Dipper hangs straight down from Polaris — as if from a nail on the north wall of the icy winter sky (per Leslie Peltier). This week the Little Dipper assumes that position around 9 p.m., depending on where you live in your time zone. By mid-January, the very coldest time of year, it's there at 7 p.m., right after dinnertime.

    Monday, December 17

  • First-quarter Moon (exact at 5:18 a.m. Eastern Standard Time).

    Tuesday, December 18

  • Mars is closest, passing 54,783,000 miles (88,165,000 km) from Earth at 7 p.m. EST. For all about observing Mars with your telescope, see the guide and surface-feature map in the November Sky & Telescope, page 66.

    Wednesday, December 19

  • This being December, the landmark constellation Cassiopeia is practically overhead after dinnertime, with its zigzag shape oriented like a flattened letter M.

    Thursday, December 20

  • The red long-period variable stars R Geminorum and T Eridani should be at maximum light (7th or 8th magnitude) this week.

  • The bright eclipsing variable star Algol should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 10:58 p.m. EST. Algol takes several additional hours to fade and to rebrighten. For all times of Algol's minima this month, good worldwide, see the December Sky & Telescope, page 78.

    Friday, December 21

  • Longest night of the year (in the Northern Hemisphere). The solstice comes at 1:08 a.m. on the 22nd EST, 10:08 p.m. on the 21st PST. This is when the Sun is farthest south for the year and begins its six-month return northward. Winter officially begins in the Northern Hemisphere, summer in the Southern Hemisphere.

  • The Moon meets the Pleiades. When dusk falls, North Americans who take a look with binoculars will see that the nearly full Moon has just finished crossing the Pleiades cluster. If you live as far northeast as the Canadian Maritimes, you can use a telescope to catch a star or two emerging from behind the Moon's bright limb. Northern Europeans get a better show; there the Moon occults the Pleiades high in the sky in late evening. See the December Sky & Telescope, page 77.

    Saturday, December 22

  • Look right of the Moon for orange Aldebaran, and farther left of the Moon for pale yellowish Capella, as shown below.

    Looking east-northeast in early evening.
    The Moon passes through bright winter constellations once it grows big and bright itself. Watch it skim closely by Mars on the 23rd. (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. For clarity, the Moon is shown three times actual size.)
    Sky & Telescope diagram

    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).

    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of maps; the standard is Sky Atlas 2000.0) 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 enchanting though increasingly dated Burnham's Celestial Handbook). Read how to use them effectively.

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

    This Week's Planet Roundup

    Mercury, Jupiter, and Pluto are "combust": an old astronomical term meaning hidden in the glare of the Sun.

    Venus (magnitude –4.1, in Libra) is the bright "Morning Star" in the southeast before and during dawn. Look for Spica, much dimmer, well off to its upper right before daylight gets too bright. Arcturus shines much farther to Venus's upper left.

    The same face of Mars as imaged by an amateur with a 12.5-inch scope (Sean Walker on Dec. 9, 2007) and by the Hubble Space Telescope (on Dec. 1). For larger views and other recent Hubble shots of Mars, which show difference faces of the planet, see the Hubble Heritage Project press release issued Dec. 18th.
    S&T: Sean Walker
    Mars is passing closer to Earth than it will again until 2016. Blazing bright yellow-orange (magnitude –1.6) in Gemini, Mars rises in twilight and is high up in fine view in the east by mid- to late evening, awaiting your telescope. It shines at its very highest around midnight or 1 a.m. — passing near the zenith, in fact, for observers at mid-northern latitudes. By dawn it's glaring lower in the west.

    Although Mars is technically closest to Earth on December 18th, the day-to-day difference is insignificant; the planet appears 15.8 or 15.9 arcseconds in diameter all this week and next. Mars will be at opposition on December 24th. For all about observing Mars with a telescope this season, see the guide and surface-feature map in the November Sky & Telescope, page 66.

    Saturn (magnitude +0.6) rises in the east around 10 or 11 p.m. and is highest in the south before dawn. Fainter Regulus (magnitude +1.4) is 9° to Saturn's upper right after they rise, and directly right of it as they fade out in dawn's glow high in the southwest.

    Uranus (magnitude 5.9, in Aquarius) is visible in the south-southwest right after dark, high above Fomalhaut.

    Neptune (magnitude 7.9, in Capricornus) is getting low in the southwest after dusk. Finder charts for Uranus and Neptune are in the July Sky & Telescope, page 60, and online.

    All descriptions that relate to your horizon or zenith — including the words up, down, right, and left — are written for the world's midnorthern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Standard Time (EST) equals Universal Time (UT, UTC, or GMT) minus 5 hours.

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