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Beautiful meteor showers
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METEOR showers (流星雨) increase in the number of meteors (流星) observed in a particular part of the sky. Meteor showers usually occur annually and with varying intensity.
An observer in the middle of the stream sees the meteors fall left and right, above and behind him. However, they all seem to come from a certain direction, or a single point. That direction is the radiant, or radiant point (辐射点).
A shower is named for the constellation (星座) in which its radiant is located, eg, the Lyrids appear to come from a point in Lyra (天琴座), the Perseids from Perseus (英仙座), and the Orionids from Orion (猎户座).
While the average counting rate of meteors for the entire sky is between five and 10 per hour, an observer may see twice this number in one part of the sky during a shower, and in the case of the Perseids, possibly more than 100 in an hour. Meteor showers are closely associated with comets (彗星). When a comet breaks up, a swarm of (群) 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 dates of these showers are accurately known, and astronomers can prepare for them in advance. Often, the comet responsible for particular showers is known: for instance, the Andromedids are associated with Biela's comet, and the Aquarids and Orionids are thought to be associated with Halley's comet.
Some of the better-known meteor showers and their approximate dates are: Lyrids, on April 21; Perseids, on August 12; Orionids, on October 20; Taurids, on November 4; Leonids, on November 16; Geminids, on December 13. (SD-Agenices)
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