Sky at a Glance | September 7th, 2012

Dawn view; the Moon is waning
By dawn, the waning Moon is high in the south with Jupiter and Aldebaran when passing through last-quarter phase. (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. The Moon is shown three times its actual apparent size.)

Friday, Sept. 7

  • Jupiter and the last-quarter Moon rise together around 11 or midnight, depending on where you live. Watch for them coming over the east-northeast horizon, and look for fainter Aldebaran to their right. They continue climbing high up the sky until dawn Saturday morning the 8th, as seen here.

    Saturday, Sept. 8

  • It's still summer, but look low in the southeast this week after about 9 p.m. (depending on where you live) and there's 1st-magnitude Fomalhaut, the Autumn Star, already making its seasonal appearance.

    Sunday, Sept. 9

  • This is the time of year when bright Vega shines closest to the zenith as the stars come out at dusk. Vega goes right through your zenith if you're at latitude 39° north (Baltimore, Kansas City, Lake Tahoe).

    Monday, Sept. 10

  • Equally bright as Vega overhead is Arcturus sinking in the west. Look a third of the way up from Arcturus to Vega for the dim semicircle of Corona Borealis, the Northern Crown, with its one moderately bright star, Alphecca. Look two thirds of the way up for the dim Keystone of Hercules.

    Watch the waning crescent Moon descend past Venus from morning to morning. The blue 10° scale is about the apparent width of your fist held at arm's length.
    Alan MacRobert

    Tuesday, Sept. 11

  • Before and during dawn Wednesday morning, Venus shines left of the waning crescent Moon, as shown here. They're 4° or 5° apart at the times of dawn for North America. Also spot Procyon farther to their right (outside the frame here). And before the sky brightens too much, binoculars show the Beehive star cluster 3° to Venus's left.

    Wednesday, Sept. 12

  • If you use a telescope, you've discovered that there's more to resolving double stars than their separation. The brightness difference between a double's two components plays a crucial role too. But how, exactly? Join a test project to find out! See Sissy Haas's article and list of test pairs in the September Sky & Telescope, page 68. Observe them carefully with your scope and report back.

    Thursday, Sept. 13

  • So you think Cygnus, despite its position in the Milky Way, has a shortage of deep-sky objects? Then you haven't seen Sue French's Deep-Sky Wonders article with photo charts in the September Sky & Telescope, page 58, and Steve Gottlieb's Going Deep article on page 63. Cygnus will never be the same.

    Friday, Sept. 14

  • As the Great Square of Pegasus rises high in the east these evenings, the Big Dipper is swinging down low in the northwest as if carrying water. To see the Dipper at its very lowest due north, you'll have to stay up till 2 a.m. daylight-saving time. Come December it'll be there at dusk.

    Saturday, Sept. 15

  • With summer nearing its end, the Teapot of Sagittarius has moved over to the south-southwest right after dark, tilting to the right as if to pour out the last of summer.


    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 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 the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope effectively.

    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 classic if dated Burnham's Celestial Handbook.

    Can a computerized telescope replace charts? I don't think so — not for beginners, anyway, and especially not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). 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 is hidden in the glare of the Sun.

    Venus (magnitude –4.3, in Cancer) rises in darkness around 3 a.m. daylight saving time (depending on where you live), emerging above the east-northeast horizon a good two hours before the first glimmer of dawn. By early dawn it's blazing high in the east.

    Binoculars show the Beehive star cluster 6° to Venus's lower left on the morning of the 8th, closing to less than 3° to Venus's left by the 12th and 13th.

    Mars and Saturn (magnitudes +1.2 and +0.8) are low in the southwest and west-southwest, respectively, as evening twilight fades. This week they widen from 13° to 17° apart. Look for them well to the lower left of brighter Arcturus in the west. Can you still find Spica twinkling under Saturn? Mars ends the week just 1° below Alpha Librae, a wide binocular double star.

    Jupiter on Aug. 23, 2012
    The side of Jupiter away from the Great Red Spot on August 23rd. South is up. The huge, reddish northern-hemisphere belt is resolving itself back into the North Equatorial Belt (NEB) and, below it here, the North Temperate Belt (NTB), with the light North Tropical Zone re-emerging between them. Notice the thin, unusual Equatorial Band in the middle of the bright Equatorial Zone.


    John H. Rogers, the British Astronomical Association's Jupiter Section director, says the recent regrowth of the NEB is its first "full-scale revival" since 1926, "and the NTB is reviving via a super-fast jet-stream outbreak as last seen in 2007. Sectors of the belts and the intervening NTropZ which were still light in June have now filled in with intense turbulence and reddish (ochre) colour, producing one
    vast brown-and-ochre belt from the NEBs to the NTB."


    Jupiter (magnitude –2.4, in Taurus) rises in the east-northeast around 11 or midnight daylight saving time. Once it's well clear of the horizon, look for fainter orange Aldebaran twinkling 7° to its right, and Beta Tauri a bit farther to Jupiter's left. By dawn this line of three stands very high in the south.

    Uranus (magnitude 5.7, at the Pisces-Cetus border) and Neptune (magnitude 7.8, in Aquarius) reach good heights in the southeast by mid-evening. 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 Daylight Time (EDT) equals Universal Time (also known as UT, UTC, or GMT) minus 4 hours.


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