this week's sky at a glance
Read the tale of the death of Comet ISON. Sigh. This might have been the week when it was at its best.
Friday, Dec. 6 The waxing crescent Moon hangs high over Venus at dusk, with the binocular double stars Alpha and Beta Capricorni to its lower right, as shown here.
The waxing Moon is high above Venus during and after dusk on Friday the 6th and higher on Saturday. (The 10° scale is about as big as your fist at arm's length.)
Saturday, Dec. 7 Earliest sunset of the year (near 40° north latitude). The longest night won't come until December 21st at the solstice, and the latest sunrise doesn't happen until January 4th.
The reason? Local Apparent Solar Time is shifting with respect to Local Mean Time during this part of the year, an effect caused by the tilt of Earth's axis and the ellipticity of Earth's orbit. Be glad that we use standard time, so you don't have to keep adjusting your clocks to the inconstant Sun like in olden days. Standard time made things simpler for society but complicated things for skywatchers.
Sunday, December 8 This evening, look to the right of the Moon by less than a fist-width at arm's length for the dim Water Jar asterism of Aquarius. Far lower left of the Moon shines Fomalhaut.
Monday, December 9 First-quarter Moon (exact at 10:12 a.m. EST). This evening the Moon shines just under the dim Circlet of Pisces below the Great Square of Pegasus. Jupiter is passing just 15 arcminutes from Delta Geminorum, magnitude 3.5, this evening and tomorrow evening. That's about half a pencil-width at arm's length. (But it's not as close as Jupiter passed by the star on October 4th, while going the other way.)
Tuesday, December 10 The eastern (left-hand) side of the Great Square of Pegasus points down at the Moon this evening.
Wednesday, December 11 Which rises first: bright Jupiter in the east-northeast, or bright Rigel in Orion's foot in the east-southeast? Both come up soon after dark. At the latitudes of New York and Denver (about 40° N), Rigel comes first tonight. As far north as Ottawa and Seattle (about 46° N), Jupiter now leads.
Thursday, December 12 The tiny black shadow of Jupiter's fast-moving moon Io crosses Jupiter's face tonight from 10:02 p.m. EST to 12:17 a.m. EST. Following soon behind is Io itself, transiting from 10:37 p.m. to 12:52 a.m. EST. In a telescope, Io is much less visible on Jupiter's bright face than its shadow is.
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 after your local moonset: in the hour before the beginning of morning twilight on the 14th. But bright meteors will show even through the moonlight earlier. 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.
The Moon brightens as it waxes to full on the night of the 16th.
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 the Moon's upper left? Easier is Aldebaran farther to the Moon's lower left. Brighter Capella shines much farther left of the Moon.
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).
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.
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.
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
Mercury (magnitude –0.7) is sinking away deep into the glow of sunrise.
Venus (magnitude –4.9) is the brilliant "Evening Star" in the southwest during and after dusk. It's shining at its brightest for the year, and it doesn't set until more than an hour after dark. In a telescope, Venus has waned to a crescent about 25% lit and has enlarged to about 42 arcseconds tall, as it swings toward us around the Sun.
Mars (magnitude 1.2, in the head of Virgo) rises around 1 a.m. By dawn it's very high in the south. In a telescope Mars is still tiny and gibbous, 5.8 arcseconds wide.
Jupiter (magnitude –2.6, in Gemini) rises in the east-northeast soon after dark, with Pollux and Castor to its left. It blazes highest around 2 a.m. In a telescope Jupiter has grown to a big 45 arcseconds wide as it nears its January 5th opposition.
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.
Saturn (magnitude +0.6, in Libra) is low in the southeast as dawn begins to brighten. Look for it then 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 in the southern sky shortly after dark. 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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