This book discusses the exploration of the Asteroid Belt. This is very difficult, because of the millions of diverse targets to visit. The sizes range from dust particles to the dwarf planet Ceres. The area of the asteroid belt was searched by astronomers in the 18th century, based on the lack of a planet at a predicted orbit by the Titus Bode Law.

Before the 1890's, astronomy depended on human observation through the telescope, and this was difficult with small objects, as compared to planets. In 1891, astro-photography began producing better results.