Some daily events in the changing sky for July 25 – August 2.

If you're in Europe or Asia, get ready for the eclipse of the Sun coming up August 1st! See the date below. Or watch the eclipse live on the web; see our article with links.


As July draws to its end, Mars, Saturn, Regulus, and Venus form a lineup that's almost evenly spaced. (The blue 10° scale is about the size of your fist held at arm's length.)

Sky & Telescope diagram

Friday, July 25

  • Last-quarter Moon (exact at 2:42 p.m. Eastern Daylight Time).
  • The modest but long-lasting Delta Aquarid meteor shower is strongest this week. It's best seen from southerly latitudes and before the first light of dawn. (Late in the week the pre-dawn moonlight will be gone.)

    Saturday, July 26

  • Jupiter's Great Red Spot (see image near bottom of page) should cross Jupiter's central meridian, (the imaginary line down the center of the planet's disk from pole to pole, around 10:48 p.m. Eastern Daylight Time. Visually, the "red" spot appears very pale orange-tan. It should be visible for at least 50 minutes before and after in a good 4- or 6-inch telescope at high power if the atmospheric seeing is sharp and steady. A light blue or green filter helps a bit. The Red Spot transits about every 10 hours 56 minutes. For all its transit times, good worldwide, see our listing or online applet.

    Sunday, July 27

  • Jupiter's moon Callisto gradually emerges from behind Jupiter's southeastern limb around 8:35 p.m. EDT. . . and then it slowly fades away into eclipse by Jupiter's shadow around 9:12 p.m. EDT. It reappears out of the shadow just as gradually nearly four hours later, around 12:56 a.m. EDT.

    For more about observing Jupiter's moons, and a listing of all events happening among them in July (good worldwide), see the July Sky & Telescope, page 62.

    Monday, July 28

  • Jupiter's Red Spot should transit around 12:26 a.m. Tuesday morning EDT; 9:26 p.m. Monday evening PDT.

    Tuesday, July 29

  • The constellation Cygnus, now high in the sky, has a reputation as being star-rich but deep-sky-object poor for small telescopes. It ain't necessarily so. Plan a telescopic tour through Cygnus's northwestern wing using the chart in the August Sky & Telescope, page 69.

    Wednesday, July 30

  • Jupiter's moon Io crosses Jupiter's face from 9:07 to 11:23 p.m. EDT, followed by Io's tiny black shadow from 9:38 to 11:55 p.m. EDT.

    Thursday, July 31

  • Jupiter's Great Red Spot transits around 10:55 p.m. EDT.

    Friday, August 1

  • New Moon, and total eclipse of the Sun for parts of the Arctic, Siberia, and China. The eclipse is partial over most of Europa and Asia. Skywatchers in easternmost Canada have a slight partial view right at sunrise. See our article — including links to live webcasts.

    Saturday, August 2

  • One day after it was eclipsed, the Moon is a hair-thin crescent very low in the west shortly after sunset, to the left of Venus. Use binoculars.
  • Jupiter's Red Spot transits around 11:33 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 is hidden in the glare of the Sun. Next week, however, it will emerge from the sunset to begin fine configurations with Venus, Saturn, and Regulus.

    Venus (magnitude –3.9) is still deep in the glow of sunset. Using binoculars, look for it just above the west-northwest horizon 20 to 40 minutes after sundown, as shown at the top of this page. Try also for much fainter Regulus nearby. Venus is slowly making its way up toward a grand "Evening Star" showing in late fall and winter.

    Mars and Saturn (magnitudes +1.7 and +0.8) are getting farther apart and sliding lower toward Venus in the evening twilight, as shown at the top of this page.

    Jupiter on July 27, 2008

    Jupiter's Great Red Spot (GRS) and, to its upper left, Oval BA ("Red Spot Junior") were approaching the planet's central meridian when Sean Walker took this image at 2:16 UT July 27th through mediocre seeing. South is up, to match the view in many telescopes.

    In recent weeks Oval BA passed by the GRS unscathed, but the newer red marking named the "Little Red Spot" got pulled into the GRS and disappeared.

    S&T: Sean Walker

    Jupiter (magnitude –2.7, in Sagittarius) shines with a steady glare in the southeast to south during evening. It's left of the Sagittarius Teapot and just below the bowl of the smaller, dimmer Teaspoon. It's highest by around 11 p.m. daylight saving time. For high-resolution scopes in excellent seeing, Jupiter's Great Red Spot and its little red companions put on an interesting performance in the last few weeks; see press release from the Hubble Space Telescope site.

    Uranus and Neptune (magnitudes 5.8 and 7.8, respectively, in Aquarius and Capricornus) are well up in the southeast by midnight. Use our article and finder charts.

    Pluto (magnitude 14.0, in the northwestern corner of Sagittarius) is highest in the south in late evening. 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 (UT, UTC, or GMT) minus 4 hours.


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