Meteoroids and meteorites
Moving around the Sun with the asteroids, comets and planets are billions of tiny pieces of rock and ice called meteoroids. They range in size from a grain of sand to a boulder. When a piece enters the Earth's upper atmosphere at speeds between 11 and 72 kilometres per second (40,000 - 260,000 km/hr), friction with the air heats the outside to more than 1000 degrees Celsius. This happens at altitudes between 80 and 100 kilometres. To an observer on Earth a streak of light is observed in the night sky and is commonly called a shooting star or a falling star. The correct name is meteor. A meteor is called a meteorite if it's large enough to survive the trip through the Earth's atmosphere and land on the ground.
Dating of meteorites collected by astronomers shows that they are 4,500 million years old, which is approximately the age of the solar system. The most common types of meteorites are stony, stony-iron and iron.
Meteoroids orbit around the Sun in either random chaotic orbits or in streams. Most streams are associated with the orbits of comets and are likely left over material from comet tails or when comets break up. When the Earth's orbit intersects a meteor stream you see an increased number of meteors called a meteor shower. Of meteors in random orbits, typically about 12 per hour can be seen at night. For meteor showers the number observed varies, but can be as high as thousands per hour. Famous meteor streams are named after the constellation that they appear in. For example the Leonids are named after the constellation of Leo and are visible around mid-November.
