Astronomy news for the week starting Friday, October 30, 1998.

The Moon passes through its full phase this week on the night of Tuesday, November 3 just about midnight as it is crossing the meridian to the south, set among the stars south of Aries. As it traverses near the ecliptic, it will first be seen to the right of Jupiter the night of Friday, October 30, and to the left of the giant planet the following night. It will then pass to the south of Saturn the morning of Wednesday the 3rd.

Farther along, the Moon will pass through the stars of Taurus the night of Thursday, November 5, and for the lucky residents of the east coast will cover or occult the bright star Aldebaran about 7:30 PM Eastern Time, with reappearance about half an hour later. Such occultations are not only fun to watch, but are astronomically useful as well. To the eye, the star, which has a terribly small angular diameter, disappears in back of the Moon or reappears with remarkable suddenness. Careful observation, however, can allow astronomers to measure the time it takes the Moon to cover the star and thereby calculate the stars's angular diameter, hence its real diameter in kilometers (which for Aldebaran is about 40 times that of the Sun).

The full Moon makes viewing the skies difficult, so why not actually look at the Moon? The dark areas readily visible to the naked eye are vast lava flows, most of which are set into enormous impact basins that are nearly four billion years old. The basins were created when large pieces of debris left over from the creation of the Solar System crashed into the lunar surface. Lava from the interior of a once-hot Moon then leaked to the outside over a period of a billion years or so. Once thought to be seas, they still bear watery names, the large one to the upper left of center called Mare Imbrium, the "Sea of Showers," which fills a basin 1100 kilometers across. Those to the right of Mare Imbrium are a set of smaller circular basins, while the large dark area at the left of the Moon, "Oceanus Procellarum," the Ocean of Storms," seems more to be runoff of lava into a low area. The Moon is now cold, all volcanic activity long gone. The craters seen through the telescope are not volcanic and were, like the basins, are holes in the ground created by impact.
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