1720: On 10 February 1720, Edmund Halley was appointed second Astronomer Royal of England.
Born in 1656, he computed in 1705 that a bright comet was periodic and would make another appearance in 1758. The comet appeared as predicted and is now known as Comet Halley.
Unfortunately, Halley died in 1742 and never saw his prediction come true. Halley pioneered our understanding of trade winds, tides, cartography, naval navigation, mortality tables, and stellar proper motions. He (incorrectly) proposed that Earth was made of concentric spheres the size of the inner planets each of which might contain life.
Perhaps Halley's greatest discovery, however, was that his contemporary Isaac Newton had discovered a powerful mathematical formulation of gravity.