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meteor shower, increase in the number of meteors observed in a particular part of the sky. The trails of the meteors of a meteor shower all appear to be traceable back to a single point in the sky, known as the radiant point, or radiant. A shower is named for the constellation in which its radiant is located, e.g., the Lyrids appear to come from a point in Lyra, the Perseids from Perseus, and the Orionids from Orion.
Meteor showers usually occur annually and with varying intensity. While the average counting rate of meteors for the entire sky is between 5 and 10 per hr, an observer may see twice this number in one part of the sky during a shower, depending on atmospheric conditions and the degree of darkness, and in the case of the Perseids, possibly more than 100 in an hour. The Leonids produce spectacular displays roughly every 33 years, as they did during the meteor storm of 1966 (with a peak of a thousand a minute) and the intense shower of 2001 (with a peak of several thousand an hour).
Meteor showers are closely associated with comets. When a comet breaks up, a swarm of particles eventually becomes scattered out over its entire orbit. If this orbit intersects that of the earth, a meteor shower will be observed. The shower will be particularly intense in those years when the original comet would have been observed. The Andromedids are associated with Biela's comet, the Aquarids and Orionids are thought to be associated with Halley's comet, and the Leonids are associated with Comet Tempel-Tuttle. Some of the better-known meteor showers and their approximate dates are: Lyrids, Apr. 21; Perseids, Aug. 12; Orionids, Oct. 20; Taurids, Nov. 4; Leonids, Nov. 16; Geminids, Dec. 13.
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