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The Perseid meteor shower occurs every year from about July 23 to August 22. The shower’s “maximum,” or time when the greatest number of meteors per hour fall, is usually August 12 or 13. The rate at which the meteors fall is determined by where Comet Swift-Tuttle is in relation to Earth when Earth crosses Swift-Tuttle’s orbit. The comet has a ring of debris in its orbit, and when this debris enters Earth’s atmosphere, the meteor shower begins. The concentration of meteors is higher when the comet is near Earth. In the early 20th century, the peak rate was as low as 4 meteors per hour. When Swift-Tuttle was very close to Earth in 1993, however, the peak rate was between 200 and 500 meteors per hour. The first record of the Perseid meteor shower comes from a Chinese manuscript written in A.D. 36. The Italian astronomer Giovanni Schiaparelli linked the Perseid shower to Comet Swift-Tuttle in 1866, four years after the comet was detected by modern astronomers.