Some daily events in the changing sky for August 29 – September 6.

Three planets in the sunset

Using binoculars, watch faint little Mars close in on Venus and Mercury lower down.

Sky & Telescope diagram

Friday, August 29

  • Look overhead right after dark this week. Shining there (if you live in the mid-northern latitudes) is bright Vega. Look west to spot equally bright Arcturus. A third of the way down from Vega to Arcturus is the dim Keystone of Hercules. Two-thirds of the way down is the dim semicircle of Corona Borealis, the Northern Crown. In Corona Borealis is one brighter star, named Alphecca, Gemma, or Diadem.

    Saturday, August 30

  • New Moon (exact at 3:58 p.m. Eastern Daylight Time).
  • Jupiter's satellite Io reappears out of eclipse from Jupiter's shadow around 11:13 p.m. EDT. In a telescope, watch it gradually swell into view barely to Jupiter's east.

    Sunday, August 31

  • If you own a telescope, you probably know that Sagittarius (now highest in the south right after dark) is full of fine deep-sky objects. But there's more here than you probably know. For a tour of some of Sagittarius's lesser-known telescopic treasures, see Sue French's Deep-Sky Wonders guide in the September Sky & Telescope, page 69.
  • Jupiter's Great Red Spot should cross Jupiter's central meridian around 10:30 p.m. Eastern Daylight Time. The "red" spot appears very pale orange-tan. It should be visible for at least 50 minutes before and after in a good 4-inch telescope if the atmospheric seeing is sharp and steady. A light blue or green filter helps. For all its transit times, good worldwide, see our listing or applet online.

    The Moon joins the bright-twilight tableau for September's first three days. (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.)

    Alan MacRobert


    Monday, September 1

  • Jupiter's moon Europa crosses Jupiter's face from 8:37 to 11:20 p.m. Eastern Daylight Time, followed by Europa's tiny black shadow from 10:49 p.m. to 1:34 a.m. EDT (best seen from western North America).

    Tuesday, September 2

  • With summer soon to change to fall, the Great Square of Pegasus is well up in the east after dark. Look for it balancing on one corner. It's a bit larger than your fist held at arm's length.

    Wednesday, September 3

  • The bright eclipsing variable star Algol should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 1:27 a.m. Thursday morning EDT. Algol takes several additional hours to fade and to rebrighten; watch it slowly dim down through the evening.

    Thursday, September 4

  • Some doorstep astronomy: Just after dark at this time of year, Arcturus shines brightly due west. Off it its right in the northwest, the Big Dipper poses at about the same height.

    Watch the bright waxing Moon cross Scorpius and Sagittarius after dark in early September. (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.)

    Alan MacRobert


    Friday, Sept. 5

  • Jupiter's Red Spot (see photo below) should transit around 9:38 p.m. EDT.

    Saturday, Sept. 6

  • Look just above the Moon in twilight for Antares sparkling orange-red. Binoculars help.
  • Venus, faint Mercury, and fainter Mars fit in a 3.8° circle from this evening through September 13th. They remain within 5° of each other through the 19th. See our article and movie (Quicktime, 1 MB).
  • Algol should be at minimum light for a couple hours centered on 10:15 p.m. EDT.

    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 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.

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

    This Week's Planet Roundup

    Mercury (about magnitude 0) is 3° lower left of much-brighter Venus low in the west-southwest in bright twilight, as shown at the top of this page. Bring binoculars.

    Venus (magnitude –3.8) is still low in the glow of sunset. Look for it above the west-southwest horizon about 30 minutes after sundown. Fainter Mercury is just to its lower left, as shown at the top of this page. Look too for little Mars, moving in day by day from the left.

    Mars (a dim magnitude +1.7!) is closing in on Venus and passes 1/3° south (lower left) of it on September 11th. See the illustration at the top of this page — and use binoculars!

    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.

    Christopher Go

    Jupiter (magnitude –2.6, in Sagittarius) shines bright and steady in the south right after dark, and lower in the southwest later. It's above the Sagittarius Teapot and just below the smaller, dimmer Teaspoon.

    Saturn is hidden behind the glare of the Sun.

    Uranus and Neptune (magnitudes 5.7 and 7.8, respectively, in Aquarius and Capricornus) are well up in the southeast during evening. Use our article and finder charts.

    Pluto (magnitude 14.0, in the northwestern corner of Sagittarius) is 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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    • About Alan MacRobert

    Alan M. MacRobert became an avid Sky & Telescope subscriber in 1966 at age 14, joined the editorial staff in 1982, and is now a senior contributing editor, semi-retired. He played a role in practically every part of the magazine and the company's other products for more than a generation, both on the amateur-observing side and the science-reporting side. In 1994 a book collection of his observing how-tos and telescopic sky tours was published as Star Hopping for Backyard Astronomers. He has produced This Week's Sky at a Glance online every week since 1989.

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