A comet's return in 1758 proved Newton's laws worked beyond the planets

In 1705, Edmond Halley noticed that comets seen in 1531, 1607 and 1682 shared the same orbit and guessed they were one object, returning roughly every 76 years. Using Newton's gravitational laws, he predicted it would come back in 1758 — and it did, spotted on Christmas Day by a farmer, 16 years after Halley's own death. It was the first confirmed proof that something other than a planet obeyed Newtonian mechanics.

— Edmond Halley, A Synopsis of the Astronomy of Comets — 1705 — public domain