Understanding Meteor Showers the Pleiades the Perseid and more

In August, in the stillness of the early dusk, take a step away from the city lights into the cool, dark night. Find a clear space where you can gaze without obstruction into the northeast, toward the darkest part of the heavens, and make yourself comfortable: for the most famous of all meteor showers will soon be blazing their sparking paths across the sky.

A meteor shower occurs when the earth’s orbit takes it through a swarm of particles, often sourcing from a comet or former comet, which in turn draws them out of the Oort cloud outside the orbit of Pluto. Meteors, also known as “shooting stars”, result from the heat of friction created when these particles encounter the earth’s atmosphere. Even a particle the size of a grain of dust can leave a bright, highly visible trail. The trails can range widely in colour, depending on the exact composition of the particle. Most vapourise completely long before they reach an altitude of 80 kilometres. Only a very few physical remnants make it all the way through the atmosphere to land on earth and become meteorites.

A few swarms, such as the August Perseids (which originate from the tail of the 109P/Swift-Tuttle comet) or the November Leonides (from the Tempel-Tuttle comet), are very well documented and highly predictable. Known in medieval Europe as the tears of St. Lawrence, the Perseids are so named because their angle of approach to the earth makes them seem to originate within the constellation Perseus. Much of the Perseid dust cloud is over two thousand years old.

While a few meteors can usually be spotted on any night, during meteor showers the frequency rises to fifteen or more per hour. Occasionally the orbit of the earth intersects a particularly dense part of the meteoric dust cloud, resulting in a meteor storm of several meteors per minutes. For the best-known meteor clouds such meteor storms are also highly predictable. The last meteor storm was that of the 2006 Perseids; the next hoped-for storm will be the Augrides at the beginning of September 2007.