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Astronomy Picture of the Day

Airplane Cloud Shadows

Photo of the Week.. Cloud tops cast spectacular shadows in a morning sunrise from 35,000 feet.

Astronomy news for the week starting Friday, November 8, 2002.

The Moonwaxes in its crescent phase the early part of the week, passing f irst quarter on Monday, November 11, about the middle of the afternoon in North America, while the Moon is climbing the daylight eastern sky. On Saturday, the 10th, the Moon passes well south (about 5 degrees) of Neptune, and on the night of Monday, the 11th, equally far south of Uranus.

The brightening of the Moon will slowly cause the washing out of the fainter stars. Curiously, even though they are the same angular size, the first quarter Moon is roughly twice as bright as the last quarter. The reason is quickly seen at full Moon even with the naked eye. The huge, dark, lava-filled impact basins (the famed " maria") that make the "Man in the Moon" and other fanciful creatures, are not evenly distributed, but lie more toward the Moon's eastern edge (or limb) than toward the western edge. As a result, they cover more of the lunar territory during third quarter than they do first quarter, and therefore shed less reflected lunar light. This uneven distribution extends around to the back, or far, side of the Moon, where the maria effectively disappear. Because the Moon rotates on its axis in synchrony with its orbital revolution, we never get to see the far side; various wobbles allow us to map about 60 percent of the Moon from the Earth. Our full knowledge of the far side comes only from spacecraft. Someday perhaps it will be a home for radio observatories, allowing them to be entirely free of interference from the Earth.

The innermost planet, Mercury, is quite out of sight, passing superior conjunction with the Sun (when it is on the other side of the Sun) on Wednesday, the 13th. Venus, however, having already passed inferior conjunction (when it is roughly between us and the Sun), is slowly becoming visible in the morning sky. By midweek, this closest planet to the Earth will be rising about the time twilight commences, and will grace the morning sky ever-more visibly for the rest of the year. Better, watch also for the ever-earlier rising of Saturn, the ringed planet coming up over the eastern horizon around 7 PM, with Jupiter following 4 hours later.

This is the season for Cassiopeia, Pegasus, and the rest of the gang from the Andromeda myth. Look high to the south around 8 PM to see the large box of stars that makes the Great Square of Pegasus. From off its northeast corner swing two graceful streams of stars that make Andromeda herself. Above the center of the figure lies the great Andromeda Nebula, Messier 31, a nearby galaxy much like ours, and at a distance of two million light years, the farthest thing that can be seen with the unaided eye. Below Andromeda lies The flat triangle that makes Triangulum, which is host to another, smaller, nearby galaxy, Messier 33, which can also be seen, though just barely, without optical aid.
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