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). The Taurids, though not intense in number of meteors, is noted for the spectacular fireballs it displays.
Most meteor showers are closely associated with comets. When a comet approaches the sun, a swarm of particles is shed along its 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 Geminids are an exception; they are associated with the asteroid 3200 Phaethon. The Andromedids are associated with Biela's comet, the Eta Aquarids and Orionids with Halley's comet, the Leonids with Comet Tempel-Tuttle, the Lyrids with Comet Thatcher, the Perseids with Comet Swift-Tuttle, and the Taurids with Comet Encke. Some of the better-known meteor showers and their approximate peak dates are: Lyrids, Apr. 21; Perseids, Aug. 12; Orionids, Oct. 20; Taurids, Nov. 4; Leonids, Nov. 16; Geminids, Dec. 13.