Sky at a Glance | August 5th, 2011

Friday, August 5

  • The Moon shines in the southwest as twilight fades. Look to its right as the stars come out for Spica and, farther on, yellower Saturn.

  • Mars, low in the east-northeast just before the first light of dawn, is passing less than 1° south (lower right) of the star cluster M35 in Gemini on Saturday and Sunday mornings. Use binoculars or a telescope.

    Saturday, August 6

  • First-quarter Moon (exact at 7:08 a.m. EDT). The Moon is in the middle of Libra, to the right of the stars of upper Scorpius.

    Sunday, August 7

  • The Moon shines in the head of Scorpius this evening, near Antares.

    Capricornus doubles
    Alpha and Beta Capricorni are 2.3° apart and fit easily into even a 15× field of view. Here they're oriented about as they appear from mid-northern latitudes soon after dark. Both are optical double stars. Alpha can often be split with the unaided eye, but Beta needs optical aid; its components appear closer together, and the fainter one is magnitude 6.0.
    Akira Fujii
  • In the southeastern sky after dusk, about a third of the way from the horizon to overhead, are the dim but distinctive stars of the western end of Capricornus. The scene is shown magnified at right, roughly as if in binoculars (but brighter). Alpha Capricorni is a wide pair, wide enough that you can probably resolve its two components with the unaided eye if you look carefully.

    Monday, August 8

  • This evening the Moon shines between the head of Scorpius to its right and the top of the Sagittarius Teapot to its left.

  • The brightest asteroid, 4 Vesta, is just past opposition this week, shining at magnitude 5.7 in Capricornus. It's an easy find in binoculars in late evening and can be seen with the unaided eye from a dark site once the Moon sets. Use the finder chart in the August Sky & Telescope, page 53, or our Vesta and Ceres finder charts online. The Dawn spacecraft is orbiting Vesta and sending back high-res pictures. Dawn will spiral down to a much lower orbit for closeup imaging by early 2012.

    Meanwhile, 1 Ceres lurks two constellations farther east in Cetus. It's magnitude 8.3 and brightening. After Dawn departs Vesta in summer 2012, it will fly on to take up orbit around Ceres in February 2015.

    Tuesday, August 9

  • Ganymede, Jupiter's biggest satellite, will disappear into eclipse by Jupiter's shadow around 3:24 a.m. Wednesday morning Eastern Daylight Time. Jupiter's Great Red Spot should cross the planet's central meridian about 44 minutes later, around 4:08 a.m. Wednesday morning EDT. The "red" spot appears very pale orange-tan. It should be visible for about an hour 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 complete Jupiter satellite phenomena and Red Spot predictions for August, good worldwide, see "Action at Jupiter" in the August Sky & Telescope, page 54.

    Wednesday, August 10

  • In late afternoon or early evening, the dark edge of the gibbous moon occults the 2.9-magnitude star Pi Sagittarii (in the Teaspoon) for the eastern half of North America. See our article. Here are timetables by city for the star's disappearance and (on the Moon's bright limb) reappearance.

    The Big Dipper high in the northwest is now dipping around into its water-holding position.
    Akira Fujii

    Thursday, August 11

  • Look west after nightfall this week for bright Arcturus shining about halfway up the sky. Turn to the right and look northwest at about the same height for the Big Dipper. The two front stars of the Dipper's bowl point upper right toward Polaris farther around to the right due north (outside the frame here). And farther around in the northeast, there's Cassiopeia at about the same height as the Dipper.

    Friday, August 12

  • The annual Perseid meteor shower peaks late tonight, but the light of the practically full Moon fills the sky all night and will hide all but the brightest meteors. See our article, Off Year for the Perseid Meteor Shower. You can look forward to next year, when the Moon will be just a waning crescent.

    Saturday, August 13

  • Full Moon (exact at 2:57 p.m. Eastern Daylight Time). The Moon is between dim Aquarius and Capricornus.


    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 sky 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

    Sun on August 5, 2011
    The Sun, with its big Spot Group 1263, as seen in the early hours of August 5th.
    SOHO / HMI

    The Sun is currently displaying a "naked eye" sunspot group; you'll only need a safe solar filter, or a #14 rectangular arc-welder's filter, to view through. Yes, the Sun is active again; my welder's glass stayed unused in the back of my desk drawer here at work for way too long!

    The spot will rotate over to the Sun's western limb in the next few days after August 5th; it will become increasingly difficult to see as we view it more edge on. Read more.

    Mercury and Venus are hidden in the glare of the Sun.

    Mars (magnitude +1.4, approaching the feet of Gemini) rises around 2 or 3 a.m. daylight-saving time. By dawn it's in good view in the east. It's the "star" far lower right of Capella and far lower left of Aldebaran. In a telescope, Mars is just a tiny blob only 4.5 arcseconds in diameter. It's on its way to a poor opposition (13.9 arcseconds wide) next March.

    Jupiter on July 31, 2011
    Jupiter on the morning of July 31st, with Callisto passing south of it, imaged by S&T's Sean Walker. The South Equatorial Belt (above center) remains wide, and the great Red Spot lacks its usual light Red Spot Hollow. The North Equatorial Belt remains narrow and darker red-brown. Walker used a 12.5-inch Newtonian telescope and an Imaging Source video camera to create this stacked-frame image.
    S&T: Sean Walker

    Jupiter (magnitude –2.5, in southern Aries) rises in the east-northeast around 11 or midnight daylight saving time. Look above it for the little star pattern of Aries and (once Jupiter is well up) closer below it for the head of Cetus, rather dim. By dawn Jupiter shines very high in the southeast.

    Saturn (magnitude +0.9, in Virgo) is sinking ever lower in the west-southwest at dusk. Look 12° left of it for Spica and 2° or 3° right or lower right of it for fainter Gamma Virginis (Porrima).

    Uranus (magnitude 5.8, in western Pisces) and Neptune (magnitude 7.8, in western Aquarius) are well up in the east or southeast by midnight. Here's our printable finder chart for both.

    Pluto (magnitude 14.0, in northern Sagittarius) is highest in the south right after dark — but this is not the week to try for it, what with the bright Moon.


    All descriptions that relate to your horizon — 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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