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This Week's Sky at a Glance

by Alan M. MacRobert

Some daily events in the changing sky for September 7 – 15.

Looking east as dawn grows bright
As the Moon wanes, it descends into the glow of dawn past Venus and the Saturn-Regulus pair. (This scene is 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.

Friday, Sept. 7

  • During dawn tomorrow morning, the waning crescent Moon poses high to the upper left of Venus, as shown here. Use Venus to guide your way with binoculars to tougher Saturn and Regulus low down.

    Saturday, Sept. 8

  • On Sunday morning the crescent Moon is left of Venus and above Saturn and Regulus, as shown at right.

    Sunday, Sept. 9

  • Uranus is at opposition (opposite the Sun in the sky).

    Monday, Sept. 10

  • Chi (χ) Cygni, one of the brightest long-period variable stars in the sky, is nearing maximum light. It's predicted to reach magnitude 5.2 around September 22nd, but last year it hit magnitude 3.7. Chi Cygni tends to alternate between bright and faint maxima — so will this year's peak be dimmer than expected? Keep track of its doings (in the shaft of the Northern Cross) using binoculars and the comparison-star chart in the September Sky & Telescope, page 58, or online. And compare your estimates to those being reported to the AAVSO.

    Tuesday, Sept. 11

  • New Moon (exact at 8:44 a.m. EDT).

  • A partial eclipse of the Sun happens for central and southern South America early this morning. Local predictions.

    Wednesday, Sept. 12

  • The shaft of the Northern Cross in Cygnus is one of the richest Milky Way regions anywhere in the sky. Take a tour through some of its telescopic treasures using Sue French's "Deep-Sky Wonders" column and sky chart in the September Sky & Telescope, page 61.

    Thursday, Sept. 13

  • Soon after sunset, use binoculars to pick up the thin waxing crescent Moon very low above the west horizon. To its right is Mercury. To its upper left is Spica. Don't wait too long or they'll set!

    Friday, Sept. 14

  • Shortly after sunset, the crescent Moon is very low in the west-southwest; use binoculars. To its right is Spica. Farther right of Spica (and probably a bit lower) is Mercury.

    Saturday, Sept. 15

  • As soon as the stars come out, look for the Big Dipper in the northwest and W-shaped Cassiopeia at the same height in the northeast. Later in the evening, the Dipper swings lower and Cassiopeia climbs higher.


    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 somewhat dated Burnham's Celestial Handbook). Read here how to use them effectively.

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



    This Week's Planet Roundup

    Mercury (magnitude 0) is deep in the glow of sunset. It's in the midst of a poor apparition for the Northern Hemisphere. Try looking for it with binoculars about 20 minutes after sundown, just above the west horizon. Don't confuse Mercury with Spica well to its upper left.

    Venus on Aug. 30, 2007
    Venus was still a very a thin crescent just 14° from the Sun when Sean Walker took this stacked video image, using a 12.5-inch Newtonian reflector, after sunrise on August 30, 2007. He boosted contrast to darken the blue sky.
    S&T: Sean Walker
    Venus (magnitude –4.4) shines low in the east at dawn, getting higher every day. A telescope shows it to be a thin crescent, but not as thin as in the image here taken August 30th. Venus is waxing in phase, as it's always doing when you see it as the "Morning Star."

    Mars (magnitude +0.2, in Taurus) rises around 11:30 p.m. daylight saving time and shines very high in the southeast before dawn. It's left or lower left of twinkly Aldebaran, which is similarly colored but not as bright. Dimmer Beta Tauri is to Mars's left.

    In a telescope Mars appears gibbous and 8.5 arcseconds in diameter, barely more than half the size it will reach around its Christmas-season opposition. The last two months of Martian dust storms seem to have abated, and though the planet's atmosphere is still bright and hazy with dust, surface features are beginning to show through a little better. But they're still low-contrast; don't expect to see much, especially with Mars still so tiny.

    Jupiter Sept. 2, 2007
    Jupiter is bidding telescopic observers a long farewell, but even so, Christopher Go caught this fine shot on September 2nd (at 10:35 UT) from his low latitude in the Philippines. North is up. The South Equatorial Belt has become a pair of narrow dark lines separated by a wide white zone (at least on this side of Jupiter). Lower right of center, South Tropical Disturbance #1 is very prominent.
    Christopher Go
    Jupiter (magnitude –2.1, in southern Ophiuchus) glares in the south-southwest during twilight and sets around midevening. Get your telescope on it as early in twilight as you can. Antares, less bright, sparkles redly 6° below Jupiter.

    Saturn (magnitude +0.7) is low in the glow of sunrise, about 16° lower left of brilliant Venus. If you pick up Saturn in binoculars or a wide-field scope, you can see that it's within 2° of fainter, twinkly Regulus (magnitude +1.4). Regulus is to Saturn's upper right.

    Uranus (magnitude 5.7, in Aquarius) and Neptune (magnitude 7.8, in Capricornus) are well placed in the southeast to south during evening. Finder charts for them are in the July Sky & Telescope, page 60, and online. Uranus is still within about 1° of the orange-red type-M star Phi Aquarii, magnitude 4.2.

    Pluto (magnitude 14.0, in the northwestern corner of Sagittarius) is highest in the south-southwest as soon darkness falls, about 16° east-northeast of Jupiter. A finder chart is in the July Sky & Telescope, page 60.

    All descriptions that relate to your horizon — 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 Daylight Time (EDT) equals Universal Time (UT, UTC, or GMT) minus 4 hours.

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