From earliest times, humankind has noticed flurries of meteors that seemed to emanate from particular points in the sky at particular times of the year. These flurries, now called meteor showers, are produced by small fragments of cosmic debris entering the earth's atmosphere at extremely high speed. Each time a comet swings by the Sun, it produces large amounts of small particles which will eventually spread out along the entire orbit of the comet to form a meteoroid "stream." If the Earth's orbit and the comet's orbit intersect at some point, then the Earth will pass through this stream for a few days at roughly the same time each year, producing a meteor shower.
Most meteors seen in meteor showers are caused by particles smaller than a grain of sand. As a result it is very rare to have any meteorites hit the ground during a typical meteor shower.
Because meteor shower particles are all traveling in parallel paths, and at the same velocity, they will all appear to radiate from a single point in the sky to an observer below. This radiant point is caused by the effect of perspective, similar to railroad tracks converging at a single vanishing point on the horizon when viewed from the middle of the tracks.
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