Sky at a Glance | September 12th, 2008

Some daily events in the changing sky for September 12 – September 20.

Use binoculars in bright twilight.
With binoculars, pick up Venus low in bright twilight and then look for much fainter Spica, Mercury, and Mars. Watch their configuration change from day to day.
Friday, September 12

  • Uranus is at opposition: opposite the Sun in our sky.

  • Jupiter's Red Spot transits around 10:26 p.m. EDT.

    Saturday, September 13

  • This week, with summer nearing its end (on September 22nd this year), the Summer Triangle is reaching its highest point overhead after dusk. As the stars come out, look for bright Vega nearly straight up (if you live in the mid-northern latitudes). To Vega's east, by two or three fist-widths at arm's length, look for Deneb. Somewhat farther down from Vega toward the southeast shines Altair, which is marked by its little sidekick star Tarazed (Gamma Aquilae) a finger's width above it.

    Sunday, September 14

  • Full Moon tonight (exact at 5:13 a.m. Monday morning EDT).

    Monday, September 15

  • Full Moon isn't when most observers turn their telescopes Moonward. But have you ever looked closely for the subtle gray shadings — and even slight colors — in the flat lunar maria? Now's the time to try! See Chuck Wood's "Exploring the Moon" column in the September Sky & Telescope, page 60.

    Tuesday, September 16

  • In bright twilight, look with binoculars for the 6° diamond of Venus, Spica, Mercury, and Mars very low in the west-southwest, as shown above.

  • Ganymede, Jupiter's largest moon, casts its shadow onto Jupiter's face from 10:41 p.m. to 2:00 a.m. EDT tonight (7:41 to 11:00 p.m. PDT). For a listing of all events among Jupiter's moons this month, visible worldwide, see the September Sky & Telescope, page 58.

    Wednesday, September 17

  • April is when the Big Dipper dumps into the Little Dipper after dark. Now with summer turning to fall, it's the Little Dipper's turn to dump into the Big Dipper at nightfall.

    Thursday, September 18

  • Right after dusk, spot bright Jupiter in the south. Then look high above it and a bit left to spot Altair. Left of Altair, by roughly a fist width at arm's length, is the dim but distinctive constellation Delphinus, the Dolphin. The Dolphin is leaping upward and bending to the left. You'll need at least a moderately dark sky; look early before the Moon rises high.

    Friday, September 19

  • If you're in eastern North America and have a clear view to the east-northeast, plan to get out your telescope and watch the waning gibbous Moon passing, and perhaps occulting, the Pleiades. See the September Sky & Telescope, page 64. Detailed predictions are available from the International Occultation Timing Association (IOTA). If you're in northern Europe, the occultations will be seen later in the night with the Moon high in the sky.

    Saturday, September 20

  • As the evening grows late, look for Fomalhaut, the Autumn Star, rising in the southeast. At the same time Arcturus, the Spring Star, is getting low in the west. They'll be at exactly the same height some time between about 9 and 10 p.m., depending on where you live in your time zone. How accurately can you time this event?

    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 wisely say, "the sky never becomes a friendly place."

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

    This Week's Planet Roundup

    Mercury (about magnitude +0.2) is sinking away below much-brighter Venus, low in the west-southwest in bright twilight, as shown at the top of this page. Try with binoculars.

    Venus (magnitude –3.8) is still low in the glow of sunset. Look for it above the west-southwest horizon in bright twilight about 30 minutes after sundown. Fainter Mercury, Mars, and Spica accompany it, as shown above. Try for them with binoculars.

    Mars (a dim magnitude +1.7!) passed 1/3° south of Venus on September 11th; now it's moving away to Venus's lower right. Binoculars required; good luck.

    The Great Red Spot was on Jupiter's central meridian when Christopher Go took this image at 13:19 UT August 27, 2008. The central-meridian longitude (System II) was 128°. Note the reddish Oval BA to the Red Spot's upper left, and the bright white point marking the start of a new rift in the dark North Equatorial Belt (below center). A more extensive white disturbance has developed in the North Equatorial Belt on the other side of the planet. South is up, to match the south-up view in many telescopes.
    Jupiter (magnitude –2.5, in Sagittarius) shines bright and steady in the south right at dusk, and lower in the southwest later. It's above the Sagittarius Teapot and below the end of the smaller, dimmer Teaspoon.

    Saturn is hidden deep in the glow of sunrise.

    Uranus and Neptune (magnitudes 5.7 and 7.8, respectively, in Aquarius and Capricornus) are in the southeast to south during evening. Use our article and finder charts or the chart in the September Sky & Telescope, page 63.

    Pluto (magnitude 14.0, in the northwestern corner of Sagittarius) is still in the south-southwest right after dark.

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


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