This weekend, the Perseid meteor shower will be at its peak. While this year's light show probably won't match the 2009 shower, when watchers could see up to 173 shooting stars an hour, the Perseids are a celestial spectacle well worth packing off to somewhere away from the glare of city lights.
The Perseids take their name from Perseus, the constellation nestled between Cassiopeia and Taurus. The meteors appear to originate from a point within Perseus, but they are actually dust shaken off from the tail of the comet Swift-Tuttle.
Swift-Tuttle makes a complete pass within its orbit every 133 years, but its dust trail hangs around for much longer. As Earth passes through the residual dust cloud, the tiny particles that hit our atmosphere streak across the sky. Usually these meteors burn up, but some make it to the ground as meteorites.
Much of the dust kicked up by the comet is thought to be thousands of years old, but scientists have found a ribbon-like filament of dust that boiled off of Swift-Tuttle's tail in 1862. That newer filament has given Earth an extra surge of meteors in recent years.
Sketchy accounts of the Perseids came from Eastern astronomers nearly 2,000 years ago - "more than 100 meteors flew thither in the morning," a Chinese observer wrote in August of 36 AD.
Yale University librarian and treasurer Edward Herrick had come close to being credited as the Western discoverer of the Perseid meteor shower, but was beaten to it by Belgian statistician Adolphe Quetelet, whose reported a great shower of meteors from August 8th to 15th in a report from the Brussels Observatory in 1836.
In the past, some Catholics called the meteor shower "the tears of St. Lawrence," after the third-century martyr whom tradition holds was barbequed by the anti-Christian Roman emperor Valerian for refusing to turn over the Holy Grail and other relics of the Church.
"The peasants of Franconia and Saxony have believed for ages past that St. Lawrence weeps tears of fire which fall from the sky every year on his fete (the 10th of August)," Herrick wrote in The American Journal of Science And Arts in 1839. "This ancient popular German tradition or superstition has been found within these [past] few years to be a fact which engages the attention of astronomers."
Swift-Tuttle is providing us with a brilliant light show, but that could come with a very deadly price. The comet's orbit comes near enough to the Earth and Moon to make astronomers nervous. The comet's orbit is very stable, but there is a slight chance of impact in 4479, when the comet could pass as close as 2.7 million miles to Earth - a trifling distance in space.
The comet has a solid nucleus of about 17 miles across. Should it strike the Earth, it's estimated to do so with 27 times the force of the object implicated in the extinction of the dinosaurs.
In his book "Impact!: The Threat of Comets and Asteroids," University of Memphis astronomer Gerrit Verschuur noted that Swift-Tuttle "has been described as the single most dangerous object known to humanity."
The comet will likely remain one of the greatest extraterrestrial threats we face for 10,000 to 20,000 years, Verschuur says.
After that amount of time, "its orbit is likely to deteriorate so that it will either fall into the sun or be thrown out of the solar system, provided it doesn't hit earth before it does that," he wrote.