This week sky

August 5-14, 2011
Friday, August 5 Asteroid 4 Vesta reaches opposition and peak visibility today. It glows at magnitude 5.6 - bright enough to see with naked eyes from a dark site and an easy target through binoculars or a telescope. The asteroid lies in south-central Capricornus, a region that rises during evening twilight and climbs highest in the south around 1 a.m. local daylight time. Although today marks Vesta's peak for the year, its appearance changes so slowly that you won't see any decline if you view it later this week. NASA's Dawn spacecraft slipped into orbit around this asteroid the night of July 15/16 and has started to return some spectacular photos.
Saturday, August 6 First Quarter Moon occurs at 7:08 a.m. EDT. By the time the Sun sets this evening for North American observers, the Moon appears almost due south and about one-third of the way from the horizon to the zenith. Our satellite then appears slightly more than half-lit.
Sunday, August 7 Although Pluto reached opposition in late June, tonight’s a good time to go out and find it. That’s because the distant world passes just 0.1° due south of the 6th-magnitude variable star Y Sagittarii, which serves as a convenient guide. Pluto glows dimly at magnitude 14.0, however, so you’ll need a 10-inch or larger telescope to spot it visually.
Monday, August 8 Around 4 a.m. local daylight time, shortly before twilight starts to paint the sky, look to the east-northeast for a bright point of reddish light. This is Mars, which shines at magnitude 1.4 among the background stars of western Gemini. Don’t confuse the Red Planet with Betelgeuse, a ruddy star in Orion that lies about 15° to Mars’ lower right and shines noticeably brighter. This morning, Mars lies slightly more than 1° north of 3rd-magnitude Eta (η) Geminorum. On Thursday morning, the planet slides a similar distance north of 3rd-magnitude Mu (μ) Gem.
Tuesday, August 9 Saturn stands about 15° high in the west-southwest as darkness falls this week. The bright star Spica in the constellation Virgo the Maiden appears 12° to its left. At magnitude 0.9, the ringed planet appears almost imperceptibly brighter than the star. If you target Saturn through a telescope, do so in early evening before it dips too close to the horizon. The planet’s globe currently spans 16" while the rings measure 37" across and tilt 9° to our line of sight.
Wednesday, August 10 Look overhead around 10 p.m. anytime this week and your eyes will fall on the brilliant star Vega in the constellation Lyra the Harp. At magnitude 0.0, Vega is the brightest member of the prominent Summer Triangle asterism. The Triangle’s second-brightest star, magnitude 0.8 Altair in Aquila the Eagle, lies some 35° southeast of Vega. The asterism’s dimmest member, magnitude 1.3 Deneb in Cygnus the Swan, stands about 25° east-northeast of Vega. Although the waxing gibbous Moon diminishes the luster of stars this week, the Triangle remains conspicuous.
Thursday, August 11 Although the Perseid meteor shower doesn’t peak until the 13th, you might consider spending a half-hour viewing it before dawn today. That’s because the waxing gibbous Moon sets shortly before 4 a.m. local daylight time, leaving a 30-minute viewing window before twilight begins. (A Full Moon will be out all night at the shower’s peak.) Under a dark sky, you can expect to see roughly 10 meteors during this Moon-free period.
Friday, August 12 Brilliant Jupiter now rises shortly before midnight local daylight time and climbs the eastern sky until dawn drowns it out. Shining at magnitude –2.5, Jupiter is the night’s brightest celestial object with the exception of the Moon. When viewed through a telescope, the giant planet’s disk spans 42" and shows plenty of cloud-top detail.
Saturday, August 13 The Perseid meteor shower peaks before dawn. Unfortunately, Full Moon also occurs today, and its bright light will drown out fainter meteors and leave the brighter ones less impressive. Instead of seeing up to 100 meteors per hour as you might in a good year, a typical observer may see only 20 to 25 per hour. Your best bet is to view in the early morning hours, when the shower’s radiant climbs high in the northeast and the Moon dips low in the southwest. Try to position yourself where a tree or building blocks the Moon and reduces its glare. Full Moon arrives at 2:57 p.m. EDT. It rises in the eastern sky just as the Sun sets and reaches its peak in the south shortly after midnight local daylight time. The Moon lies in the northeastern corner of the constellation Capricornus the Sea Goat.
Sunday, August 14 This summer’s brightest comet, C/2009 P1 (Garradd), slides from Pegasus the Winged Horse into Delphinus the Dolphin this week. Both Saturday and Sunday nights are good times to look because the comet passes just north of the Dolphin’s pretty diamond-shaped body. Although the Moon lies some 35° south of the star group, it should show up nicely through binoculars. You’ll likely need a telescope to spot the comet’s 7th-magnitude glow.