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.