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Photo of the Week. September is here.

Astronomy news for the week starting Friday, September 5, 2008.

The Moon begins our busy week as a fat waxing crescent as it heads towards first quarter on Sunday, September 7. It thereafter grows and brightens in the waxing gibbous towards full, which it will not reach until next week. The early part of this week sees it moving gloriously against the background of the two deep southern constellations of the Zodiac, Scorpius and Sagittarius. The night of Friday the 5th finds the Moon to the west of the Scorpion's three-star head. The next evening (Saturday the 6th), the Moon comes into close conjunction with (just to the south of) bright reddish Antares. Two nights later, on Monday the 8th, the Moon will be shifted northwest of the Teapot of Sagittarius, and then the following night (Tuesday the 9th) it takes on Jupiter, which will lie to northwest of the Moon (the two having passed conjunction during the day). An hour after the Moon passes first quarter, it also passes apogee, where it is farthest from the Earth.

The early evening twilight sky contains a remarkable, though largely invisible, grouping of three planets, Venus, Mercury, and Mars, the latter the dimmest and without optical aid quite invisible. Try, though, to find the brightest, Venus, which climbs a bit higher each night. On Wednesday the 10th, Mercury hits greatest eastern elongation, though the low tilt of the ecliptic makes it hard to see below and to the left of much brighter Venus. At nearly the same time, Mercury and Venus come into formal conjunction four degrees apart, while on the following two days both of them pass conjunction with Mars.

Then, rather oddly, it's on to the greatest and smallest of planets, Jupiter and Pluto. (Is Pluto a "planet?" The semantic argument still rages. It is what it is, the nearest and almost biggest within the band of debris beyond Neptune called the "Kuiper Belt." Perhaps from its history, we can call it an "honorary planet.") Jupiter, just above the Little Milk Dipper of Sagittarius, ends its retrograde motion (westerly against the stellar background) on Sunday the 7th, and then begins its long slow climb toward Capricornus. The following day, that of Monday the 8th, Pluto (also in Sagittarius roughly 15 degrees to the northwest of Jupiter and near the border with Ophiuchus) does the same thing. But while brilliant Jupiter is easily seen to the south as twilight draws to a close (not setting until around midnight), Pluto, 1500 times fainter than the faintest star visible to the naked eye, requires a decent telescope to see.

After admiring early evening's Scorpius and Sagittarius, lift your eyes upward to the Summer Triangle of Vega (nearly overhead), Deneb (at the top of Cygnus's Northern Cross), and Altair (a bit south). Following along behind Cygnus will be the Great Square of Pegasus, telling us that autumn is not far behind and that the summer gang will soon be gone.
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