Perseids Meteor Shower
Perseids Meteor Shower — Like most meteor showers, the Perseids are caused by comet debris.
As comets enter the inner solar system, they are warmed by the sun and peppered by the solar wind, which produces the familar tails that stretch across the night sky when a bright comet is close to Earth.
Comet tails are made of tiny pieces of ice, dust, and rock which are spewed into interplanetary space as they bubble off the comet’s nucleus. When Earth encounters these particles on its journey around the Sun, they strike the atmosphere speeds exceeding 100,000 mph. (The average speed of Perseid meteoroids is 130,000 mph!) M
ost are observed as a bright streak across the sky that can last for several seconds, but occasionally a large fragment will explode in a multicolored fireball. Most of the streaks (popularly called ‘shooting stars’) are caused by meteoroids about the size of a grain of sand, but much less dense.
Although they travel at high speeds, these tiny meteoroids pose no threat to people or objects on the ground.
The Perseids were the first meteors ever associated with a particular comet. From 1861 to 1863, observers noted a great increase in the number of August Perseids. As many as 215 per hour were seen in 1863.
The Italian astronomer Giovanni Virginio Schiaparelli (better known for giving the name “canali,” or “channels,” to the dark linear markings on Mars) calculated the orbits of some Perseid meteoroids and discovered that they closely matched that of periodic comet Swift-Tuttle, which had been discovered in 1862 during its close approach to Earth.
Swift-Tuttle orbits the Sun once every 135 years. The last time it passed near Earth was in December 1992. The proximity of the comet once again caused an increase in Perseid activity and, in August 1993, observers in Central Europe were treated to 200 to 500 meteors per hour.
Swift-Tuttle won’t make another swing through the inner solar system until 2126, but when it does the comet itself is expected to be an impressive sight as seen from Earth, rivalling Comet Hyakutake in 1996 or Comet Hale-Bopp in 1997.