Sky at a Glance | July 24th, 2009

Some daily events in the changing sky for July 24 – August 1.

Facing west after sunset. Binoculars help.
After sunset, the waxing crescent Moon helps guide the way to Saturn, Regulus, and Mercury. Binoculars help when you're looking for faint things in a sky this bright. (The Moon is positioned for a skywatcher near the middle of North America. In Europe, move each Moon symbol a quarter of the way toward the one for the previous date. In the Far East, move it halfway. The blue 10° scale is about the size of your fist held at arm's length.)

Friday, July 24

  • The waxing crescent Moon hangs below Saturn at dusk, as shown above.

    Saturday, July 25

  • Look for Saturn upper right of the Moon.

  • This evening through Monday evening, Saturn is passing less than 1/3° north (upper right) of the 4th-magnitude star Sigma Leonis, Leo's hind foot. Use binoculars or a telescope at low power.

    Sunday, July 26

  • This week the annual Delta Aquarid meteor shower is at its most active, very late at night. Under ideal observing conditions from a southerly latitude before dawn, you might count about 20 meteors per hour. The numbers will be lesser elsewhere.

    Monday, July 27

  • The red long-period variable stars V Bootis, R Bootis, and S Hydrae should be about at maximum light (7th or 8th magnitude) this week. V Boo is easy to locate with binoculars less than 1° from 3rd-magnitude Gamma Boo; see the comparison-star chart for it in the July Sky & Telescope, page 54.

    Tuesday, July 28

  • First-quarter Moon (exact at 6:00 p.m. Eastern Daylight Time).

    Wednesday, July 29

  • Got a big scope and a dark sky? Explore the Abell 2199 galaxy cluster, off the Keystone of Hercules, using the charts and travel guide in Ken Hewitt-White's "Going Deep" column in the July Sky & Telescope, page 61.

    Thursday, July 30

  • Antares shines left of the waxing gibbous Moon after dusk (as seen from the longitudes of the Americas).

    Facing east in early dawn
    Venus outshines all else in the eastern sky as dawn begins. 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.

  • Mars has been passing not far from similar-looking Aldebaran in the pre-dawn sky this week, as shown at right.

    Saturday, August 1

  • The Eagle Nebula (or Star Queen Nebula) in Serpens Cauda became an astronomical icon with the Hubble image, released in 1995, of its "Pillars of Creation." The nebula and its associated star cluster look quite different in an amateur scope. Many lesser clusters and nebulae also swarm in its vicinity. Explore them all with Sue French's "Deep-Sky Wonders" column and sky chart in the August Sky & Telescope, page 59.


    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, 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'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

    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
    Mercury (about magnitude –0.6) 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. Watch Mercury closing in fast on fainter Regulus, to Mercury's upper left. They'll be just 0.6° apart on the evening of August 2nd.

    Venus and Mars (magnitudes –4.0 and +1.1, respectively, both in or near Taurus) are in the east during dawn. Venus is a dazzler; Mars, well to Venus's upper right near Aldebaran, is 110 times fainter. They're moving farther apart: from 13° to 16° separation this week.

    Aldebaran, similar to Mars in both brightness and color, twinkles about 5° or 6° to Mars's lower right or right. Higher above them are the Pleiades. Far left of them shines bright Capella. And look lower right of Venus for Orion.

    Jupiter (magnitude –2.8, in Capricornus) shines low in the east-southeast during twilight. It's higher in better telescopic view around midnight.

    The impact on Jupiter. A black dust mark, like those of the Comet Shoemaker-Levy 9 impacts in 1994, appeared suddenly in Jupiter's south polar region around July 18th. It's now spreading out. Backyard observers have been spotting it in 4-inch scopes during moments of good atmospheric seeing. See our article.

    Jupiter and Neptune on July 9, 2009
    On the morning of July 9th, Bob Kimmel of Rockledge, Florida, took this image of Jupiter (overexposed) and Neptune when they were 1/2° apart. Why are they so different in brightness? Jupiter is a bigger planet, but mostly it's because Jupiter is closer to the Sun (so it gets lit more brightly) and closer to Earth.


    Kimmel used an 8-inch f/5 Newtonian reflector with a Canon D20a DSLR camera body on his back patio. This is an unguided 20-second exposure at ISO 3200.

    Bob Kimmel
    Saturn (magnitude +1.1, in Leo) is getting low in the west after sunset, as shown at the top of this page. Look early! Saturn's rings are narrowing, appearing only 2° from edge on. And they're getting very dim. The rings turn edge-on to the Sun and go black on August 10th. They 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) remains about 1½° from Jupiter, but it's 17,000 times fainter. See our finder charts for Uranus and Neptune.

    Both of these outermost planets show a very pale blue-green tint in a medium-size to large telescope, if your eye is particularly sensitive to color. Otherwise, or in a smaller telescope, they're basically gray.

    Pluto (14th magnitude, in northwestern Sagittarius) is highest in the south just after dark. See the finder chart in the June 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.


    "Rational and innocent entertainment of the highest kind."
    — John Mills, 19th century Scottish manufacturer and founder of Mills Observatory, on amateur astronomy.


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