They are tiny bits of rocky space debris left in the orbital wake of Comet Swift-Tuttle. Each year around Aug. 12, the Earth crosses the orbit of Swift-Tuttle and plows into the stream of debris. Most of the particles are the size of grains of sand. These particles hit our atmosphere at about 40 miles per second and are heated to white-hot temperatures. Unless the meteor is a really big one, it's completely consumed in the atmosphere.
Larger meteors can sometimes fall to Earth intact where they are called meteorites.
The Perseids are just one of several meteor showers that happen throughout the year, but their impressive numbers and bright meteors make it a favorite to watch. Meteor preparedness Like most astronomical events, memorable observing of the Perseid shower belongs to the folks who make the most effort to see it. If your observing session consists of looking out your windshield while driving home at 10 p.m. that night, you can expect next to nothing. Observers under clear, dark rural skies who wait until 11 p.m. to get started and hang until dawn may be rewarded with a count of hundreds of meteors. If you're up for more than a windshield view but not quite an all nighter, the Perseids are still worth watching.