Sky at a Glance | July 31st, 2009

Some daily events in the changing sky for July 31 – August 8.

Facing east in early dawn
Venus outshines all else in the early eastern dawn this week. Mars is more on a par with some of the bright stars in this early preview of "winter" constellations.

Friday, July 31

  • Look for Antares shining to the right of the gibbous Moon after dusk (as seen from the longitudes of the Americas). The Moon occults (covers) Antares as seen from much of southern Asia and, in daylight, the Middle East; map and timetables.

  • Venus blazes left of Orion in the dawn this week, as shown at right, while Mars and Aldebaran look on from above.

    Saturday, August 1

  • This evening the Moon floats like a big bright bubble just ejected from the spout of the Sagittarius Teapot.

    Sunday, August 2

  • Binoculars show Regulus just 0.6° below Mercury very low in the west in bright twilight about a half hour after sunset, as shown below.

    Monday, August 3

  • Jupiter occults (passes across) the 6th-magnitude star 45 Capricorni for observers in Europe and easternmost North America. It's quite rare for a planet to occult such a bright star. And there are a bunch of other telescopic events around Jupiter this week. See our article.

    Tuesday, August 4

  • At this time of year, the Big Dipper hangs diagonally in the northwest after dark. Its handle arcs around leftward to point toward bright Arcturus at about the same height in the west.

    Looking west in bright twilight
    Bring binoculars to pick little Mercury and Regulus out of the sunset very low in the west. Good luck!
    Wednesday, August 5

  • Full Moon (exact at 8:55 p.m. EDT), with Jupiter near it. The Moon undergoes a very slight penumbral eclipse, probably too slight for any shading to be detectable at all by eye. If you want to try, South America, Europe, or Africa are the places to be; the midtime is 0:39 August 6th UT.

    Thursday, August 6

  • The Moon rises in the dusk with baleful Jupiter just 4° to its right.

    Friday, August 7

  • If you live near latitude 39° north (Washington DC, Cincinnati, St. Louis, Kansas City, Lake Tahoe), bright Vega passes right through your zenith sometime between about 10 and 11 tonight — depending on how far east or west you live in your time zone.

    Saturday, August 8

  • The waning gibbous Moon is up in the east by the time twilight fades to dark. Look off to its upper left for the Great Square of Pegasus now standing on one corner.


    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 each issue of Sky & Telescope diagram" target="new_window">Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    Sky Atlas 2000.0 (the color Deluxe Edition is shown here) plots 81,312 stars to magnitude 8.5. That includes most of the stars that you can see in a good finderscope, and typically one or two stars that will fall within a 50× telescope's field of view wherever you point. About 2,700 deep-sky objects to hunt are plotted among the stars.
    Alan MacRobert
    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts; 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 more detailed and descriptive 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? 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 and a curious mind." Without these, "the sky never becomes a friendly place."

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


    This Week's Planet Roundup

    Mercury (about magnitude –0.4) is having a poor apparition deep in the glow of sunset. Look for it very low in the west-northwest in bright twilight, as shown at the top of this page. Binoculars help.

    UV Venus
    The new white spot is arrowed in these ultraviolet stacked-video images of Venus taken by Frank Melillo a few minutes apart.
    Frank Melillo
    Venus (magnitude –4.0, in the feet of Gemini) blazes in the eastern sky before and during dawn.

    As recently happened with Jupiter, an amateur planetary imager has found a newly-appeared marking on Venus! Frank Melillo of Holtsville, New York, discovered that Venus had unexpectedly grown a "Great White Spot" in ultraviolet light when he imaged it on the morning of July 19th, as shown here. Other amateur ultraviolet imagers soon confirmed it. The European Space Agency's Venus Express probe, currently orbiting Venus, has imaged the spot in detail. See New Scientist article for more.

    Mars (magnitude +1.1, in the horns of Taurus) is well to the upper right of Venus before dawn. Not far to Mars's right or upper right is Aldebaran, a close match for it in both brightness and color. The two are 7° apart on August 1st, 10° apart by the 8th.

    Jupiter's impact scar is the small dark mark in the planet's South Polar Region (top). The black dot on the edge of the South Equatorial Belt is the shadow of Callisto. Note the Great Red Spot just about to rotate out of sight on the celestial west limb (left). Sky & Telescope's Sean Walker used a 14.5-inch reflector for this stacked-video image 8:45 UT July 23, 2009.


    The impact mark is near System II longitude 210°. To find the times of its future central-meridian crossings, add 2 hours and 6 minutes to our listed times of the Great Red Spot's transits. At least that's its approximate location; it may be moving a bit in longitude.

    S&T: Sean Walker
    Jupiter (magnitude –2.8, in Capricornus) shines low in the east-southeast during twilight. It's higher in better telescopic view in the southeast by midnight.

    The impact on Jupiter. A black dust marking, like those made by the Comet Shoemaker-Levy 9 impacts in 1994, appeared suddenly in Jupiter's south polar region around July 18th. Since then it has been elongating. Backyard observers have been spotting it in 4-inch scopes during moments of steady atmospheric seeing. See our article.

    Saturn (magnitude +1.1, in Leo) is getting very low in the west after sunset. Look early!

    Saturn's rings may have vanished by the time you read this. They turn edge-on to the Sun and go black on August 9–10, visible only in silhouette against the planet's globe as a black hairline (if you get lucky with good atmospheric seeing). The rings turn edge-on to Earth on September 4th, but by then Saturn will be lost in the sunset.

    Uranus (magnitude 5.8, just below the Circlet of Pisces), is high in the south before dawn.

    Neptune (magnitude 7.8, in Capricornus) appears about 2° from Jupiter, but it's 17,000 times fainter. See our finder charts for Uranus and Neptune.

    Pluto (14th magnitude, in northwestern Sagittarius) is highest in the south just after dark. See the finder chart in the June Sky & Telescope diagram" target="new_window">Sky & Telescope, page 53.

    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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