Perseids meteor shower explained: comet Swift‑Tuttle origins and eye optics behind star‑shaped images

Each August, the Perseids meteor shower dazzles observers as Earth crosses the dust trail left by comet 109P/Swift‑Tuttle. The comet, a 26‑km icy body moving at about 60 km/s, last passed close to Earth in December 1992 and will not return until 2126. Its debris produces 50‑100 meteors per hour, peaking in mid‑August and coinciding with the August 12 solar eclipse.

The number of points seen in the star‑shaped caustic images of bright stars varies between viewers. This variation is caused by individual eye aberrations, which are mathematically described by Zernike polynomials. Different combinations of these polynomials alter the symmetry order of the caustic, leading some people to perceive six‑pointed stars while others see eight or more.