ABSTRACT
The Minor Planets or Asteroids are small bodies, all below 1000 km in diameter. Most of them occupy the ‘Main Belt’, between the orbits of Mars and Jupiter. A systematic search for a planet orbiting between the paths of Mars and Jupiter was initiated in 1800 by six astronomers meeting at Lilienthal, where Johann Schroter had his observatory. Taking the Earth’s distance from the Sun as 10 units, the remaining figures give the mean distances of the planets with reasonable accuracy out to as far as Saturn, the outermost planet known in 1772. Most of the asteroids which invade the inner reaches of the Solar System are very small indeed. The absolute magnitude of an asteroid is the apparent magnitude that it would have if seen from unit distance at full phase. In 1906 Max Wolf, from Heidelberg, discovered asteroid 588, Achilles, which was found to move in the same orbit as Jupiter.
