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Skylights featured nine times on Earth Science Picture of the Day: 1 2 3 4 5 6 7 8 9 -- Full List Restored!


Photo of the Week.. The fully eclipsed Moon of October 8, 2014, sets in early morning twilight. See a somewhat later view with the Moon deeper into Earth's shadow.

Astronomy news for the week starting Friday, October 10, 2014.

After full Moon and the glorious total eclipse last Wednesday morning, the Moon fades this week in its waning gibbous phase, finally passing third quarter on Wednesday, October 15, about the time of Moonset in North America. Look for it in the morning sky when it is so close to the actual quarter that you cannot tell the difference. We thereafter see a little bit of the waning crescent as our companion dives toward new Moon and a partial eclipse of the Sun late next week.

In the third century B.C., 2300 years ago, Aristarchus of Samos actually made an estimate of the ratio of the distance of the Sun to that of the Moon by observing the angle between the Moon and the Sun at the time of the quarters. If the Sun is infinitely far away, the angle should be exactly 90?. The closer the Sun, the smaller the angle. Aristarchus found an angle of 87? and announced that the Sun is 20 times farther from the Earth than is the Moon. Unfortunately, his method is impossible to apply with any accuracy because the Sun is so far away (20 times more distant than he thought), and because the true angle is so close to 90? that it cannot be discriminated from a right angle. His result was produced by simple (and understandable) observational error. Nevertheless, the idea is ingenious, and even if his measurement was wrong, his conclusion of enormous distance was correct. ("Astronomy!" HarperCollins 1994, copyright J. B. Kaler)

Though Saturn is effectively gone, lost to twilight, Mars drifts along to the east against the background stars to the east of Antares between Scorpius and Sagittarius almost as far south of the celestial equator as the planet can get (nearly 25 degrees) and not setting until an hour and a half after the sky is fully dark. Then around 2 AM Daylight Time, Jupiter makes its dazzling appearance popping up above the eastern horizon, the giant planet on the border between Cancer and Leo to the west of Leo's luminary, Regulus, and very obvious as the sky lightens. On Thursday the 16th, Mercury passes inferior conjunction with the Sun, the little planet more or less between us and the Sun (though not crossing it) and quite invisible.

By mid-evening, the Summer Triangle of Deneb, Vega, and Altair (the Triangle's southern anchor) is slipping to the west of the celestial meridian, while Pegasus, with its Great Square, lies to the east of that north-south line. Not quite 30 degrees to the east of Altair, find Enif, the bright western leader of the celestial Horse. Just to the west of Enif, in a dark sky you might spot the small ragged rectangle that makes Equuleus, the "Little Horse, which frisks just to the southeast of Delphinus, the Dolphin.

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