What is meteor?
In ancient times, objects in the night sky conjured superstition and were associated with gods and religion. But misunderstandings about meteors lasted longer than they did about most other celestial objects.
Meteorites (the pieces that make it to Earth) were long ago thought to be cast down as gifts from angels. Others thought the gods were displaying their anger. As late as the 17th century, many believed they fell from thunderstorms (they were nicknamed "thunderstones"). Many scientists were skeptical that stones could fall from the clouds or the heavens, and often they simply didn't believe the accounts of people who claimed to have seen such things.
In 1807, a fireball exploded over Connecticut, and several meteorites rained down. By then the first handful of asteroids had been discovered, and a new theory emerged suggesting meteorites were broken bits off asteroids or other planets. (A theory that still holds.)
One of the most significant meteorite events in recent history destroyed hundreds of square miles of forest in Siberia on June 30, 1908. Across hundreds of miles, witnesses of the Tunguska event saw a ball of fire streak through the sky, suggesting the meteor entered the atmosphere at an oblique angle. It exploded, sending out hot winds and loud noises and shook the ground enough to break windows in nearby villages. Small particles blown into the atmosphere lit the night sky for several days. No meteorite was ever found, and for years many scientists thought the devastation was caused by a comet. Now, the prevailing theory holds that a meteor exploded just above the surface.
The largest meteorite recovered in the United States fell in a wheat field in southern Nebraska in 1948. Witnesses saw a giant fireball in the afternoon that some said was brighter than the sun. The meteorite was found buried 10 feet deep in the ground. It weighed 2,360 pounds.
The most famous meteorite crater in the United States is misnamed Meteor Crater. It's in Arizona, and it's huge. The rim rises 150 feet from the surrounding plain, and the hole is 600 feet deep and nearly a mile wide. It was the first crater that was proved to be caused by a meteorite impact, which occurred between 20,000 and 50,000 years ago.
When a comet nears the sun, a trail of dust and other debris burns off and remains in solar orbit. As Earth orbits the sun, it passes through this debris field spread across its path. Small bits burn up in the atmosphere, creating meteors. Meteors come from other sources, too, but comet debris streams are the source of sometimes dramatic meteor showers.
When to watch
The part of Earth where dawn is breaking is always at the leading edge of our planet's plunge along its orbital path around the Sun. This part of the planet tends to "catch" oncoming meteors left by a comet, whereas the other side of Earth, where it is dusk or late evening, outruns the debris. For that reason, the hours between midnight and dawn are typically the best time to watch a meteor shower. A meteor sometimes explodes above the surface, causing widespread damage from the blast and ensuing fire. This happened in 1908 over Siberia.