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Astronomy Picture of the Day


Photo of the Week.. A rare aurura lights deep southern Texas skies against the backdrop of the Little Dipper and a Perseid meteor. Photo courtesy of Chris Grohusko. (This image also appeared as the Astronomy Picture of the Day for September 15, 2000.)

Astronomy news for the week starting Friday, September 6, 2002.

We begin the week and the first of the September Skylights with the new Moon. Almost exactly one day past new, on Saturday the 7th, the Moon will pass perigee, where it is closest to the Earth, the common coincidence causing especially high tides at the coasts. The slim crescent will become visible by the night of Sunday the 8th, when it lies in southwestern evening twilight just up and to the left of Mercury, affording a fine chance to locate the elusive planet, which is especially shy at this elongation from the Sun, as the ecliptic now lies so flat against the horizon. The night of Monday, the 9th, the growing crescent will be found up and to the right of brilliant Venus, which itself is an unmissable sight again in southwestern twilight. That evening, the Moon, Venus, and the star Spica will make a near-perfect equilateral triangle, with hard-to-see Spica at the lowest apex, down and to the right of the Moon. Be sure to admire the outline of the Moon's nighttime side, which will be gently illuminated by Earthlight. First quarter will be reached next Friday, September 13.

The planetary sky is oddly symmetrical. While the evening sky holds the two inner planets, the morning sky remains the domain of the giants, Saturn in Taurus, and Jupiter in Cancer. Jupiter is now making a fine passage just to the south of the faint, but naked-eye, "Beehive" cluster of stars, known also as the Praesepe, or M44. The night of Friday the 6th, Jupiter will be directly south of the cluster, and by the end of the week notably to the southeast, the cluster providing a good way to observe how the planets really do move against the starry background. Many such clusters dot the sky, the best of them the Pleiades and Hyades in Taurus (to the west of Saturn), and even the central part of the Big Dipper in Ursa Major. In between the inner planets and the two giants lie the two outer planets, Uranus (now near the Capricornus-Aquarius border) and Neptune, which still lies deep in Capricornus. Such symmetries come and go and mean nothing physically. Mercury will soon be gone from the evening sky and enter the morning sky, and in another eight years, Jupiter and Saturn will be opposite each other.

The approach of fall is augured by the late-evening sightings of the autumn stars. As Scorpius slips away to the west and Vega and then Deneb move past the zenith, watch for the rising of the Great Square of Pegasus. As the Big Dipper moves off into the deep northwest on its perpetual journey about the pole, it is replaced by the "W" of Cassiopeia rising in the northeast. Between the two lies Polaris, which sits practically at the pole and appears unmoving to the naked eye, the Little Dipper standing nearly upright from it.
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