meteor

Flash of light in the sky, popularly known as a shooting or falling star, caused by a particle of dust, a meteoroid, entering the atmosphere at speeds up to 70 kps/45 mps and burning up by friction at a height of around 100 km/60 mi. On any clear night, several sporadic meteors can be seen each hour. A brilliant meteor is termed a fireball. Fragments found on the ground on the rare occasions when part of a meteoroid survives its passage through the atmosphere are called meteorites.

Several times each year, the Earth encounters swarms of dust shed by comets, which give rise to a meteor shower. This appears to radiate from one particular point in the sky, after which the shower is named. For example, the Perseid meteor shower in August appears to radiate from the constellation Perseus. The Leonids shoot out from the constellation Leo and are caused by dust from the comet Tempel-Tuttle, which orbits the Sun every 33 years. The Leonid shower reaches its peak when the comet is closest to the Sun.

Most meteoroids are smaller than grains of sand. The Earth receives an estimated 16,000 tonnes of meteoric material every year.

The largest field of impact craters on Earth was discovered in 2004, near the Gilf Kebir plateau of the Sahara desert. The field covered an area of 5,000 sq km/1,930 sq mi and was thought to be about 50 million years old.