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First quarter

Photo of the Week. Daylight first quarter with tree. (This photo has been added to Moonlight.)

Astronomy news for the week starting Friday, August 21, 2009.

The waxing crescent Moon comes up this week out of the evening horizon murk and twilight. First becoming barely visible the evening of Friday the August 21st, it grows through the week until it passes first quarter on Thursday the 27th in the early morning out of sight for North America, so it will be a bit past the quarter and into waxing gibbous by that evening. The evening of Friday the 21st, the Moon will pass well to the south of Saturn, which -- now setting in mid- twilight -- is effectively out of sight. Just a few hours later, and again out of sight, the Moon also passes to the south of Mercury. Pretty much setting with Saturn, the little planet is near-impossible to see, even though it reaches its greatest eastern elongation on Monday the 24th. The tilt of the evening ecliptic, which lies flat against the horizon this time of year, is very much against good Mercurian visibility.

The Moon puts on a much better show in Scorpius and surroundings. The evening of Wednesday the 26th, just before the quarter, look for it to the west of Antares and just to the right of Scorpius's three-star head, which will be nearly vertical to the horizon. Then during the late afternoon of Thursday the 27th, the Moon will pass over Antares for an invisible occultation. By the time the sky darkens, the Moon will have shifted a bit to the east of the star, providing us with a fine sight indeed.

Jupiter, now a superb evening object, makes up for the obscurity of Saturn and Mercury. Just past opposition with the Sun, it rises just before sunset, making it wonderfully visible in the southeast as the sky grows dark. Crossing the meridian to the south just after midnight Daylight Time, this second brightest planet (after Venus) does not set until after the onset of morning twilight.

Well before Jupiter-set, Mars and Venus enter the scene. Approaching Gemini from Taurus, the red planet now rises just before local midnight (around 1:30 AM Daylight Time), with Venus following around 3:30 AM or so as it zips along from Gemini into Cancer.

As summer moves towards fall, the Big Dipper of Ursa Major slides down the northwestern sky to be replaced by autumn's Cassiopeia, which is beginning to climb up in the northeast. Below (south of) the Dipper, the constellations become more and more lost into twilight, the great stack of them continuing with Canes Venatici's pair of stars, the cluster of Coma Berenices, huge Virgo with Spica, box-like Corvus the Crow, Hydra's (the Sea Serpent's) tail, and for residents of the southern hemisphere Centaurus and Crux, the Southern Cross.
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