Meteors: Quick and Easy
Meteors are rock/metal chunks that break from asteroids. They hurl through space at incredible speeds. When they hit ground, they either burn up or make a crater.
A meteor, also known as a shooting star, is a mass of stone or metal that enters the Earth's atmosphere from outside space with enormous speed. While still in space, the particles are called meteoroids. A large bright meteor is referred to as a fireball, and an exploding fireball is called a bolide. Larger meteors are not completely burned up in the Earth's atmosphere. They may form METEORITE CRATERS, such as those found on the Moon, the inner planets, and the satellites of Mars and Jupiter. It has been estimated that micro meteorites may add 1,000 tons to the mass of the Earth each day.
Although 500 large meteorites may fall on the Earth each year, only about one percent of these are recovered. More than 120 impact sites have been identified. Meteorites, which are pieces of rocks from space, have always collided with the earth. Enormous craters are proof that very large meteors have struck the earth in the distant past. It's very possible, some think, that a massive meteor measuring six to nine miles wide may have hit the planet sometime at the end of the Cretaceous Period. The force of the impact from such a meteor would have created a crater nearly 100 miles wide. It also would have made an enormous explosion, sending huge amounts of dust and debris into the atmosphere. In a very short time, the skies around the world would have been covered by a blanket of dust, blotting out much of the sun's rays. This could have lasted for several months or even years.
Although a few meteors can be seen on any night, especially after midnight, during certain times of the year so many are visible that they are termed meteor showers. Records of meteor showers exist before the 11th century. Until the present century, when the origin of such showers began to be understood, the phenomenon was usually the cause of considerable fear. Most meteor showers are believed to be produced by the debris of comets, which leave a trail of particles behind them as they orbit the Sun. When the Earth intercepts this stream of comet debris, the small particles strike the atmosphere at speeds between 22 and 60 miles a second, causing them to vaporize and create the visible meteor display. The average size of a meteor, which can be estimated from its brightness, height, and distance, is about the size of a grain of sand.
During a shower, meteors appear from a point in the sky, called the radiant, which can be associated with a particular constellation. These radiant points give each shower its name; so the Perseids, July 25-August 18, appear to radiate from the constellation Perseus, and the Leonids, November 15-19,from Leo. During the height of the heaviest showers, from 30 to 70 meteors may normally be seen every hour, but on rare occasions in a spectacular display that number may be visible every second.