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Blue sky

Photo of the Week. A white cloud, punctuated by a distant bird, enhances the color of the blue sky.

Astronomy news for the week starting Friday, September 2, 2011.

Welcome to September, where we will find the first day of fall, the Sun passing the Autumnal Equinox on the 23rd. It's a quiet week punctuated by a fine event. The Moon starts us off with a fat waxing crescent hovering over the early-evening south-southwestern horizon. With the ecliptic (the plane of the Solar System) rather flat against the evening horizon, as the Moon passes first quarter on Sunday, September 4 (around the time of Moonrise in North America), it does not get much higher as the evenings progress. The evening of Saturday the 3rd, the Moon will be a bit shy of the quarter, while the next night it will be seen a bit past it. The Moon then heads into its obvious waxing gibbous phase as it heads towards full early next week.

The evening of Saturday the 3rd, for those south of a line from the northeastern US through Texas the Moon will occult, or pass over, bright Delta Scorpii (Dschubba), the middle star of Scorpius's head and a fine eruptive variable that some ten years ago hit nearly first magnitude. For residents mostly of the southern and southeastern US, the star will disappear behind the Moon's dark leading edge around 9:30 PM CDT, give or take 15 or so minutes depending on location. For northerners and the rest of the country and Canada, the Moon will glide just to the south of the star. The following evening, that of Sunday the 4th, look for the orbiting Moon to be up and to the left of reddish Antares, while the night of Monday the 5th, the Moon will bottom out near the Winter Solstice in Sagittarius.

Setting before the end of twilight, Saturn is pretty much out of it, which leaves three planets to make the nightly scene. Rising dramatically in the east, Jupiter , up by 10 PM, tops them all, the giant planet now crossing the meridian to the south just as dawn begins to light the eastern sky. Then, just after 2 AM Daylight Time, Mars makes its appearance in the northeast still against the stars of Gemini, now just to the east of Delta Geminorum and to the south of Castor and Pollux. Number three is Mercury, the little planet now making an appearance in the east just after dawn's start and passing its greatest elongation west of the Sun the night of Friday the 2nd. The morning of Friday the 9th, Mercury will rise less than a degree to the northeast of Leo's Regulus, the planet much the brighter.

With the Moon getting brighter, the early-evening Milky Way (descending from Cygnus through Aquila and Scutum to Sagittarius) fades away. Look then for the Big Dipper going down in the northwest and for the "W" of Cassiopeia rising in the northeast, the two rounding the pole -- and Polaris -- opposite each other.
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