Neptune: The last giant

Abstract

With the discovery of Uranus, the Solar System once again seemed complete. A search through old records going back to the seventeenth century revealed that the first Astronomer Royal, John Flamsteed, had observed Uranus on no fewer than six occasions from 1690 onwards, without realizing that it was a planet rather than a star. Armed with this invaluable positional information that extended over more than one Uranian year, it seemed to be relatively straightforward to determine the planet’s orbit.