Asteroids are sometimes called minor planets.They are lumps of rock orbiting the sun, mostly in the asteroid belt between the orbits of mars & jupiter.
The first largest asteroid, ceres, is 936km in diameter & was found on new new year's day 1801.Since then thousand have been founed .Twelve of them are more then 250km in width & 26 are larger then 200km in diameter. As telescope have improved more and more smaller astroied have been detected .There are probably about 100,000 asteriod larger then 1k in diameter. Some experts think ther may be as many as 1.2 million.
Vesta the fourth asteriod to be discovered in 1807, is the only one bright enought to be seen whithout a telescope.
Astronomer belive that, on average , one astroied larger the 0.4km strikes earth every 50,000 years. some 65million years ago a 10km diameter astroied crashing to earth may have been responsible for wiping out the dianasour. It would have caused a catastrophic explosion, affecting the climate and chemical composition of atmospher and destroying the plants and animals on which the dianasour fed. As recently as 1991 a small astroied cam within 170,600km of earth, the closet recorded near miss. On 30 jan 2052 an asteriod is predicted to pass as close as 19,678km
Toutastis (asteriod 4,179) was discovered in 1989. It is named after the celtic god toutatis, whose named is used as an oath by the cosmic stripe character Asterix the gaul. Toutatis measures 4.6 by 2.4 by 1.9km. It passes earth every four year and is one of the largest space object to come so close to us. On 29 september 2004 Toutatis came within 1,555,818km of earth.Its next visit was on 9 november 2008, when it came within 7,524,773km.
