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radiant:see meteor showermeteor 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.
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radiant(ray -dee-ănt) The point on the celestial sphere, usually given in the coordinates right ascension and declination, from which a meteor appears to originate. Shower meteors all seem to radiate from this point and the trains of a series of shower meteors, extrapolated backwards, intercept at the radiant. Its position is found by calculating the intercept with the celestial sphere of the vector sum of the meteor's velocity vector and the Earth's velocity vector on collision. The radiant position changes slightly with time as the Earth moves through the meteoroid stream. Meteor showers are usually named after the constellation that contains the radiant.
the point on the celestial sphere that appears to be the source of the meteors observed when the earth encounters a swarm of meteoroids moving around the sun in a common orbit. Meteoroids belonging to the same swarm have almost exactly parallel trajectories in space. Consequently, if the paths of the meteors in the corresponding meteor shower are extended backward to the celestial sphere, they intersect in a small area of the sky because of the effects of perspective. The center of this area is the radiant.