The Perseids occur annually from July to August, peaking one night in August. They're debris from the Swift-Tuttle comet. Most pieces are more than 1,000 years old. When the Earth passes through the comet's dust trail, any bits of ice and dust that get caught in the Earth's atmosphere disintegrate, creating the streaks you see. Humans have observed the shower for at least 2,000 years, according to NASA.