Sky at a Glance | September 26th, 2008

Some daily events in the changing sky for September 26 – October 4.

Looking west in bright twilight
Watch the Moon wax in the west from night to night, passing Venus and fainter Antares. (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.)

Friday, Sept. 26

  • With fall under way, Perseus is rising up the northeastern sky in late evening. The bright eclipsing variable star Beta Persei, Algol, should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 11:56 p.m. Eastern Daylight Time Friday evening. Algol takes several additional hours to fade and then to rebrighten. (For all times of Algol's minima this month and next, good worldwide, see the October Sky & Telescope, page 68.)

    Saturday, September 27

  • Jupiter's moon Ganymede emerges from eclipse out of the planet's shadow around 8:02 p.m. Eastern Daylight Time. A small telescope will show it swelling into view just east of the planet. (The other three Galilean moons are to Jupiter's west.)

    Sunday, September 28

  • The red long-period variable star W Lyrae should be nearing its peak brightness (8th magnitude) this week. Follow its doings with binoculars or a small telescope and the chart in the October Sky & Telescope, page 67.

    Monday, September 29

  • New Moon (exact at 4:12 a.m. EDT).

  • Algol should be at minimum brightness for a couple hours centered on 8:44 p.m. EDT.

    Tuesday, September 30

  • The tiny black shadow of Jupiter's moon Io crosses Jupiter's face from 8:27 to 10:42 p.m. EDT. Io itself emerges from in front of Jupiter (on the planet's western limb) at 9:24 p.m. EDT.

  • Have you ever seen the Fly Swatter in Delphinus? It's in the same telescopic field of view as Delphinus's best double star. See Sue French's Deep-Sky Wonders column in the October Sky & Telescope (page 71) for more on this and other telescopic treasures of little Delphinus.

    Wednesday, October 1

  • In early twilight, look west-southwest below Venus for the thin waxing crescent Moon, as shown at right.

    Thursday, October 2

  • Slowly, gradually, Jupiter's outer Galilean moon Callisto slides into eclipse by the planet's shadow, with the fadeout centered on 9:29 p.m. EDT. Callisto emerges from the shadow back into view just as slowly around 1:40 a.m. Friday morning EDT (10:40 p.m. Thursday evening PDT).

    Friday, October 3

  • In twilight, look for summery Antares still glimmering barely in view. It's upper left of the Moon, as shown above.

    Saturday, October 4

  • Antares twinkles to the right of the Moon.


    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 is hidden in the glare of the Sun.

    Venus (magnitude –3.8) is gradually becoming more visible after sunset. Look for it above the west-southwest horizon in bright twilight, 30 to 45 minutes after sundown.

    Mars (magnitude +1.7) is lost in the sunset (to Venus's lower right).

    Even though Earth is pulling away from Jupiter as the season advances, Christopher Go in the Philippines took another of his suberb stacked-video images on September 28th. The Great Red Spot had crossed the central meridian less than an hour earlier; the image was taken at 10:24 UT, when the System II central-meridian longitude was 148°. Note the white rift in the South Equatorial Belt (above center) and the narrower white rift in the narrower North Equatorial Belt. South is up, to match the south-up view in many telescopes.
    Jupiter (magnitude –2.5, in Sagittarius) shines in the south in twilight, and lower in the southwest later. It's above the Sagittarius Teapot and below the end of the smaller, dimmer Teaspoon.

    Saturn glows low in the east at dawn. (Don't confuse it with twinkly Regulus higher up.) Despite the poor atmospheric seeing so low down, a telescope will show that Saturn's rings have turned nearly edge on! They're tilted just 4° to our line of sight.

    Uranus and Neptune (magnitudes 5.7 and 7.8, respectively, in Aquarius and Capricornus) are in the southeast and 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. If you've got a big scope and a dark sky, use our article and finder chart.

    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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