OT: Neuer Komet

verfasst von Popeye, 13.04.2002, 06:39

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Comet Ikeya-Zhang is enlivening the skies

READERS in the northern hemisphere, particularly those living in
the countryside, might care to glance towards the constellation
Cassiopeia over the next few weeks. Thereabouts, on clear nights,
they will see a comet known as Ikeya-Zhang, after its
co-discoverers, Kaoru Ikeya, of Japan, and Zhang Daqing, of
China. This comet, which has sprouted a satisfactorily hairy tail
(the word"comet" is derived from the ancient Greek for"hair")
made its closest approach to the sun on March 18th, and will be
closest to the earth (a mere 60m km away) on April 30th.

This is not, it seems, comet Ikeya-Zhang's first visit to the sun.
Diligent work by archivists suggests that it made a previous
appearance in 1661. That would give it an orbital period of 341
years-the longest yet measured and far longer than, for example,
comet Halley, which goes around the sun in a sprightly 76 years.
Those periods, though, are measurable only because they are
short enough for astronomers to have seen the comets in question
more than once. Most comets have orbits far longer than this.
They arrive unannounced, then disappear for hundreds of
thousands of years. As far as humanity is concerned, they are
one-shot wonders.

A comet's natural habitat is the Oort cloud, a reservoir of icy
bodies left over from the solar system's formation 4.5 billion years
ago, which is believed to stretch out for more than a light year
from the sun. Only when a comet arriving from the Oort cloud has
its orbit tweaked by a close encounter with a planet does it settle
into a more regular existence. Either that or, if the tweaking is in
the wrong direction, it gets ejected from the solar system
altogether.

For the non-astronomically minded, Cassiopeia is a"W"-shaped
formation of stars on the opposite side of the Pole Star from the
Plough (or Big Dipper, for readers in North America). Field glasses
will help, but the comet should remain visible to the naked eye
until the middle of May, at least.
Quelle: Economist

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• OT: Neuer Komet - Popeye, 13.04.2002, 06:39