Any clear night displays its quota of meteors. But at certain times, when the earth happens to collide with a stream of cosmic debris moving in an elliptical orbit, a shower of meteors takes place. (For a list of the major night meteor streams, see TABLE I.) Most meteor streams probably result from the breakup of comets; if the debris is distributed uniformly in the comet’s orbit, a meteor shower occurs each time the earth crosses the orbit. For example, the Perseids, fragments of Comet 1862 III, have reappeared every August for more than 1200 years, and the Leonids, debris of Comet Temple (1866 I), regularly return around the third week in November. Like the Taurids, another dependable stream, the Leonids are notable for their brilliant fireballs, which have deposited some of the largest meteorites ever found on the earth. Some regular showers produce great numbers of meteors at intervals of several years. For nearly a millennium, A.D. 902 to 1866, a marked increase in the number of Leonids occurred every thirty-three years. The display in 1833 was one of the most spectacular in history, and witnesses said that the “stars were falling” as thick as snowflakes. Before the scheduled major shower of 1899, however, the main stream was deflected by passing close to the planet Jupiter and the periodic spectacle did not take place. Since then, the Leonids have been considered a “lost” stream, but some members of the shower have continued to appear each November. On November 16 and 17, 1961, they produced an unexpectedly awesome display with many brilliant fireballs. TABLE I MAJOR METEOR STREAMS