Sky at a Glance | August 13th, 2010

Friday, August 13

  • Low in the west in twilight, look for the crescent Moon hanging at a tilt. It's about 10° left of Venus (for North America), as shown above.

    Perseid meteor over Stellafane
    A bright early Perseid meteor streaked down over the Stellafane convention in Springfield, Vermont, on August 7th. Click for larger view.
    Credit: Sky & Telescope / Dennis Di Cicco

  • The predicted peak of the Perseid meteor shower came last night, and sure enough, the zenithal hourly rate was running about 70 or 80. That's more than a meteor a minute for someone with ideal viewing conditions. But don't quit yet! The shower continues to trail off for several days more. The later in the night you watch, the better.

    Track the shower's continuing progress with the International Meteor Organization's near real-time activity profile, which is based on reports being sent in by the IMO's visual observers worldwide. And here are several pages of Perseid photos at Spaceweather.com.

  • Jupiter's Great Red Spot should cross Jupiter's central meridian (the imaginary line down the middle of the planet's disk from pole to pole) around 11:18 p.m. Eastern Daylight Time. Here's a list to print out of all the Great Red Spot's predicted transit times for the rest of 2010.

    Saturday, August 14

  • Arcturus is the brightest star high in the west after dusk, high above the place where Venus declines and sets in twilight. At about the same height in the northwest, look for the Big Dipper now turning right-side up. Equally high in the northeast, W-shaped Cassiopeia is climbing.

    Sunday, August 15

  • Soon after dark at this time of year, Vega crosses nearest the zenith. Whenever this happens, Altair is high in the southeast with its little companion Tarazed almost directly above it. And the Sagittarius Teapot is at its best lower in the south.

    Monday, August 16

  • Mars remains within 2° above bright Venus this evening through Friday evening. They're both moving rapidly eastward against the stars, so their positions with respect each other change only slowly.

  • First-quarter Moon (exact at 2:14 p.m. Eastern Daylight Time).

    View at dusk
    The waxing Moon crosses Scorpius on Tuesday and Wednesday. (These scenes are drawn for the middle of North America. European observers: move each Moon symbol a quarter of the way toward the one for the previous date. For clarity, the Moon is shown three times actual size.)

    Tuesday, August 17

  • Look near the Moon this evening for Antares, as shown here. They're only 1° or 2° apart as seen from most of North America.

    Wednesday, August 18

  • This evening the Moon forms a nearly equilateral triangle with Antares to its right and the Cat's Eyes pair in Scorpius's tail (depending on your location and time), as shown here.

  • The bright eclipsing variable star Algol should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 2:29 a.m. Thursday morning EDT; 11:29 p.m. Wednesday evening PDT. Algol takes several additional hours to fade and to rebrighten. Use our comparison-star chart. For all times of Algol's minima this month, good worldwide, see the August Sky & Telescope, page 62.

    Thursday, August 19

  • Neptune is at opposition tonight, opposite the Sun in Earth's sky.

    Friday, August 20

  • Good asteroid occultation: in the early-morning hours of Saturday, an 8.4-magnitude star near Aldebaran (in the loose star cluster NGC 1647) will be occulted for up to 10 seconds by the large asteroid 16 Psyche, magnitude 11.1, along a wide path from Texas to Virginia. Maps, times, and finder charts.

    The asteroid-occultation community eagerly seeks accurate timings of such events, especially by video, which is more precise than eyeball timings. Read up on timing methods. If you get involved in this addictive pursuit, join the busy discussion at the occultation Yahoo Group.

    Saturday, August 21

  • Algol should be at minimum light for a couple hours centered on 10:18 p.m. EDT, when it will be visible from the East Coast low in the northeastern sky.


    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

    .jpg" url_large="" alt="Moon, Mars, Venus, Saturn" caption=""Conjunction over Massebesic Lake": Moon, Mars, Venus, and Saturn on Aug 13, 2010. "Fed the mosquitos quite well on the beach tonight," writes S&T's Sean Walker from New Hampshire." credits="S&T: Sean Walker" width="" height="" align="left"]

    Mercury is now lost in the glow of sunset.

    Venus (magnitude –4.4) is the bright Evening Star sinking low in the west during twilight.

    Mars and Saturn (magnitudes 1.5 and 1.1, respectively) are near brilliant Venus low in twilight. Mars slowly skims a few degrees above Venus this week, while Saturn moves increasingly far off to Venus's right or lower right. Look carefully; Mars and Saturn are less than 1% as bright as the dazzler.

    Left of this group, look for Spica. Very high above them shines brighter Arcturus.

    Jupiter with Red Spot and Red Spot Jr., Aug. 13, 2010
    By August 13th, Jupiter's Oval BA (Red Spot Junior) had nearly caught up with the Great Red Spot and was about to pass it. Also note the ghostly tan and blue-gray signs of the broad South Equatorial Belt hidden under white clouds. These traces now include the outline of the Red Spot Hollow just below the spot. South is up.


    Christopher Go took this stacked-video image at 18:03 UT Aug. 13, 2010.

    Alan MacRobert

    Jupiter (magnitude –2.7, in Pisces) rises around the end of twilight and is well up in the east-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.

    Uranus (magnitude 5.8, in Pisces) is less than 3° west of Jupiter. In a telescope Uranus is only 3.6 arcseconds wide, compared to Jupiter's unusually wide 48″.

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

    Pluto (magnitude 14, in northwestern Sagittarius) is highest in the south right after dark, but the Moon reenters the evening sky this week. 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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