Meteor shower is the entry into the Earth's atmosphere of a number of meteoroids at approximately the same place and time, traveling in parallel paths and apparently having a common origin. Many meteor showers are associated with comets. Some showers return annually, others at greater intervals, irregularly or not at all, depending on the relative positions of the shower orbits and Earth's orbit.
A meteor shower's name is derived usually from that of the constellation (or of a star therein) in which is situated the shower's radiant--i.e., the point in the sky at which perspective makes the parallel meteor orbits seem to originate. Some showers (e.g., the Bielids, now called Andromedids) are named for an associated comet. The Cyrillid shower of 1913 had no radiant (it seemed to enter the atmosphere from a circular orbit around the Earth) and was named for St. Cyril of Alexandria, on whose feast day (February 9) it was observed. The great Leonid meteor shower of Nov. 12, 1833, in which hundreds of thousands of meteors were observed in one night, was seen all over North America and initiated the first serious study of meteor showers. It was later established that the Leonid shower recurred at 33-year intervals, and occasional records of its appearances were traced as far back as AD 902. Since about 1945, radar observations have revealed meteor showers regularly occurring in the daylight sky, where they are optically invisible.
Excerpt from the Encyclopedia Britannica without permission.