They are galactic residue of comet Swift-Tuttle which every 130 years sweeps in from deep space beyond the planet Pluto. The comet hurtles through the plane of our solar system not far (but far enough not to pose a threat) from Earth's orbit.
The first reported sighting of the Perseids was in the Chinese annals in 36 AD when "more than 100 meteors flew thither in the morning."
How does the shower happen?
Comets are giant snowballs with stellar dust frozen inside. The comet's ice traps the dust. But as a comet travels close to our sun, the ice particles heat up. They become gases (just think of dry ice) pulled along in the comet's tail.
As the ice is transformed into gas, dust particles in the ice escape and float free. The particles continue to orbit in the gravitational field of the comet, following it like the wake from a ship spreading farther and farther from the comet. The result is a band of tiny particles traversing the sun in an enormous elliptical ring.
And every year, as the Earth crosses this ring, the dust particles burn up, incandesce, when they collide with the atmosphere, causing the phenomenon we marvel at a meteor shower.
The point of impact between the earth's orbit and the meteors' orbit is called the radiant. The Perseids' radiant, occurs close to the constellation Perseus (hence their name), just below the constellation Cassiopeia, the ancient queen fated to remain seated on her throne for eternity. You can easily identify her as a large W on its side.
The impact takes place some 80 miles above Earth's surface. And before the dust particles are five times the height of our highest-flying commercial aircraft, they "flame out."
Since they are only dust particles, this also means they will not cause the life-ending impacts Hollywood has made so much of lately.