Johannes Kepler was the first to postulate the existence of a hidden planet between Mars and Jupiter, a theory long pondered by astronomers. Then, in 1766, Johannes Titius (1729-1796), a professor of mathematics and physics in Germany, developed a formula for calculating planetary distances that seemed to suggest a planet belonged between Mars and Jupiter. When the planet Uranus was discovered in 1781, it fit into the formula, causing many scientists to be even more certain a hidden planet existed. One astronomer, Franz Xaver, proposed the formation of a society of astronomers that would be responsible for looking in assigned areas of the sky for the mystery planet.

One man, Father Giuseppe Piazzi (1746-1826), was involved in such a search at this time. During the night of New Year 's Eve, 1800, he saw a small star in Taurus. Since he could not find it listed in star catalogues, he observed...