The Comet Swift-Tuttle, which was first spotted in 1862, is thought to be roughly six miles across. Since its first official sighting in the 19th century by Louis Swift and then by Horace Tuttle three days later, this comet hadn’t been seen again until 130 years later when its closest pass with Earth occurred in 1992. It is estimated that at the most recent pass, the comet was a mere 110 million miles from the planet. It won't be seen again until 2126.
While it is rare to see the comet itself, every year, millions of people head out in search of some of the darker places of the night to witness the Perseid Meteor shower, an annual event that occurs when the Earth crosses the orbit of the comet.
Known also as the "Tears of St. Lawrence", the Perseid meteor shower takes place in mid August. While the Perseids usually peak somewhere between August 11 - 13 every year, shooting stars can often be seen a week or two before and after the peak date. Known as the most brilliant of annual meteor showers, the Perseids, at its peak, can emit anywhere from 50 to 150 shooting stars an hour.
In an excerpt from "Cosmic Collisions", Sally Stephens explains that the Comet Swift-Tuttle, continuing its 130 year journey to orbit the sun, loses its ice to a gas conversion as it nears the heated star. The process sends streams of debris and dust to trail behind it. "When the Earth crosses the orbit, at the same time each year, it plows through the dust, unleashing a meteor shower".
The Perseids were named such because the shower emerges from the constellation Perseus, a cluster of stars named after the Greek hero who slew Medusa. Medusa was said to turn all who looked at her into stone. Within the constellation, some believe that Perseus is holding the head of Medusa in his hand.
Space.com sums up the physical details of the tiny meteoroids entering the earth's atmosphere as traveling "at roughly 133,200 mph. Most are the size of sand grains; a few are as big as peas or marbles" with the consistency of cigar ash.
Meteoroids are the debris sloughed off from comets. When they reach the Earth's atmosphere and burn up, they are referred to as meteors; otherwise known as shooting stars. Those that hold together and actually reach the Earth's surface are known as meteorites.
It was once calculated that the Comet Swift-Tuttle was on a collision course with Earth, suggesting that an impact was likely to occur in the year 2026. That theory was quickly debunked as recalculations of the nearly dual century data showed differently. The new theory is that in the year 3044, the Comet Swift-Tuttle will brush by within a million miles of the Earth, considering this future event to be a true 'cosmic near miss' by astronomers.
While meteor showers are a spectacular event for viewers, they have been known to disrupt satellites, spacecraft and short out electronics. In 1994, a hole was punched in the Hubble Space Telescope by a meteoroid from the Leonid meteor shower. Currently, there are an estimated 2500 satellites in Earth's orbit.
