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A distant look at Comet Halley.



A distant look at Comet Halley

Out of sight to the naked eye but not out of astronomers' minds or the reach of Earth-based scientific instruments and telescopes, Comet Halley remains under intense scrutiny. Last April and May, astronomers from the European Southern Observatory European Southern Observatory (ESO), an intergovernmental organization for astronomical research with headquarters in Garching, near Munich, Germany. The ESO began in 1962 as a consortium among Belgium, Denmark, France, Germany, the Netherlands, and Sweden.  (SEQ SEQ Sequence
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), using the Danish telescope at La Silla, Chile, captured images of the comet, then about 1,250 million kilometers from Eart or roughly where the orbit of Saturn lies. The comet was so faint that the scientists needed to combine more than 60 images obtained over 19 nights, an exposure totaling nearly 12 hours, to see details of the comet's structure.

The resulting picture is the most detailed ever obtained of a comet so far from the sun. The comeths avocado-shaped nucleus appears as a small, bright point, which varies in brightness, reflecting rotation of the nucleus. This core appears to one side of a relatively bright, asymmetric region called the inner coma, about 120,000 kilometers across. The somewhat darker outer coma, is at least 300,000 kilometers across. The shape and density of the inner coma indicate the comet's nucleus is still releasing dust, which is pushed away from the comet by the solar wind solar wind, stream of ionized hydrogen—protons and electrons—with an 8% component of helium ions and trace amounts of heavier ions that radiates outward from the sun at high speeds. .

"The comet is still active, even at this distance," says ESO's Richard M. West, of Garching, West Germany West Germany: see Germany. . ESO ESO European Southern Observatory
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 astronomers expect to make further observations in early 1989 and in 1990, when Comet Halley will be 1,900 million kilometers away. "Not only may such observations provide a firmer basis for the determination of the rotation $(period$) of the nucleus, they also carry cometary research further into the outer reaches of the solar system solar system, the sun and the surrounding planets, natural satellites, dwarf planets, asteroids, meteoroids, and comets that are bound by its gravity. The sun is by far the most massive part of the solar system, containing almost 99.9% of the system's total mass.  than ever before attempted," he says.
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Author:Peterson, Ivars
Publication:Science News
Date:Aug 13, 1988
Words:282
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