Sky at a Glance | July 30th, 2010

Western view after sunset
Four planets shine in the western twilight. One dazzles; the others appear tiny by comparison. Watch them changing positions day by day! (The visibility of faint objects in bright twilight is exaggerated here.)

Friday, July 30

  • As twilight fades, how soon can you spot bright Venus in the west? How soon after that can you spot Saturn and Mars, much fainter, to Venus's upper left? This evening Mars is less than 2° below Saturn. Use binoculars to try for Mercury and fainter Regulus much farther to Venus's lower right.

    Saturday, July 31

  • Saturn and Mars remain close together upper left of Venus at dusk, as shown above.

    Sunday, August 1

  • Bright Vega crosses nearest your zenith around 11 p.m. daylight-saving time, depending on how far east or west you live in your time zone. Whenever Vega is nearest the zenith, you can count on the Teapot of Sagittarius, rich in deep-sky objects, to be at its highest in the south.

    Monday, August 2

  • Last-quarter Moon tonight (exact at 12:59 a.m. Tuesday morning EDT).

    Tuesday, August 3

  • Look east before dawn for the Pleiades 3° or 4° lower left of the waning Moon (as seen from North America).

    Wednesday, August 4

  • Vega and Lyra shine very high during evening for observers at mid-northern latitudes. Do you know Lyra's two Messier objects? The Ring Nebula, M57, is familiar and easy to find. But what about the globular cluster M56? See Gary Seronik's Binocular Highlight article and chart in the August Sky & Telescope, page 45.

    Thursday, August 5

  • No less than eight globular clusters pepper the area around the spout of the Sagittarius Teapot. Ferret them out with your telescope these evenings using Sue French's Deep-Sky Wonders column and chart in the August Sky & Telescope, page 64.

    Friday, August 6

  • Starting this evening, Mars and Saturn spend more than a week sliding just above brilliant Venus low in the west as twilight fades.

    Saturday, August 7

  • Venus, Mars, and Saturn are gathered most tightly this evening, fitting in a circle 4.8— in diameter — just small enough to qualify as a "planetary trio," a grouping within a 5° circle.

    Planets low in the twilight
    Venus remains the bright landmark for shy Mars and Saturn after sunset.

    Sunday, Aug. 8

  • Watch the Venus-Saturn-Mars triangle as it changes shape day by day in the western twilight. Spica too is now moving in on the scene from the left, as shown here. Can you also make out Gamma Virginis, magnitude 2.7? For this one you'll probably need binoculars.

  • Have you seen any early Perseid meteors yet? The peak of the annual shower is expected to arrive next Thursday night, the night of August 12-13. Start planning now! See our article Dark Nights for the Perseids.


    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 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 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 must have a detailed, large-scale sky atlas (set of charts). The standards are the
    Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger and deeper Uranometria 2000.0 (stars to magnitude 9.75). And read how to use your charts effectively.

    You'll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the more detailed and descriptive Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.

    Can a computerized telescope take their place? I don't think so — not for beginners, anyway, and especially not on mounts that are less than top-quality mechanically. 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."


    This Week's Planet Roundup

    Mercury (magnitude +0.1) is very low in bright twilight. About a half hour after sunset, look for it near the horizon due west, well to the lower right of bright Venus. Binoculars will help.

    Venus (magnitude –4.3) is the bright Evening Star sinking low in the west as twilight fades. In a telescope, Venus now appears almost exactly half lit.

    Mars (magnitude +1.5) is close to Saturn, upper left of brilliant Venus in twilight. Early in the week Mars is to Saturn's lower left. By week's end it's a little farther directly left of Saturn, as shown above.

    Jupiter on July 31, 2010
    The side of Jupiter away from the Great Red Spot is still showing only very thin, broken traces of the South Equatorial Belt (SEB). The SEB is normally about as wide and dark as the North Equatorial Belt, seen here below center. The SEB probably still exists but is hidden under a new layer of white, high-altitude ammonia clouds. These clouds could start to clear at any time, allowing a view once again of the belt below.


    S&T's Sean Walker took this image from New Hampshire on the morning of July 31st, at 7:47 UT. The satellite at lower right is sulfury Io.

    S&T: Sean Walker

    Jupiter (magnitude –2.7, in Pisces) rises around the end of twilight and shines high in the southeast by midnight. It's highest in the south before dawn — the brightest starlike point in the morning sky.

    Jupiter's Great Red Spot is near System II longitude 150°. Assuming it stays there, here's a list to print out of all the Great Red Spot's predicted transit times for the rest of 2010.

    Saturn (magnitude +1.1) is the slightly brighter of the two planets upper left of Venus in evening twilight. (The other is Mars.)

    Uranus (magnitude 5.8, in Pisces) is 3° west of Jupiter. In a telescope Uranus is only 3.6 arcseconds wide, compared to Jupiter's 46″.

    Neptune (magnitude 7.8, at the Aquarius-Capricornus border) is up in good view by late evening. See our finder charts for Uranus and Neptune in 2010.

    Pluto (magnitude 14, in northwestern Sagittarius) is highest in the south after dark — and now the Moon is gone. See our big Pluto finder charts in the July Sky & Telescope, page 60.


    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 (also known as UT, UTC, or GMT) minus 4 hours.


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