Word: halley
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Dates: during 1990-1999
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...thousands of miles across, is the comet's head, the light-reflecting shroud that turns an otherwise insignificant iceberg into a brilliant object. Just how brilliant depends on many factors. The solid comet's size is one, and Hale-Bopp, an estimated 20 miles across, is bigger than most. (Halley's was less than half as large.) Its history is another. Out in deep space, a comet can get encrusted with a layer of gummy dust. This layer can seal in most of the ice and prevent it from vaporizing. Some gas may spurt out through cracks in the crust...
...block too many times. The first visit loosens a comet's crust, making later go-rounds more impressive. If the comet comes through too often, however, a new crust can form out of dust falling back onto the surface. This too can lead to false optimism. "With Comet Halley, which has been back many times," says University of Texas astronomer Anita Cochran, "only about 15% to 20% of the surface is active." Admits Hale: "It's been kind of nerve-racking to sit through all those months wondering if the comet would fizzle...
...were celestial brooms wielded by the gods to sweep the heavens free of evil. In the West they were believed to presage the fall of Jerusalem, the death of monarchs and such anomalies as two-headed calves. The Norman Conquest of England was attributed to the 1066 flyby of Halley's, history's most famous comet, which has been linked to everything from Julius Caesar's assassination to the defeat of Attila the Hun. Told that Earth would pass through Halley's tail during its 1910 visit, many Americans panicked and bought gas masks and "comet pills...
...astronomer from Harvard, then a tiny school in the wilderness of the New World, sent his observations of what would later be called Halley's comet to Isaac Newton. Newton used this data from Harvard in his Principia, beginning a long tradition of astronomical excellence at the New England school, including the attendance of Edwin Hubble, the most famous astronomer of the 20th century...
That makes it the closest comet since 1983 and gives it a leg up on visibility (Halley's came no nearer than 39 million miles). Better yet, Hyakutake's trajectory will place it high in the northern sky when it reaches peak brightness this week, so that it will be visible for most of the night over most of the northern hemisphere...