Comet Observed Across Europe

1680

A great comet, the brightest since before anyone remembered, appeared in the night sky of late 1680 and remained visible for months. Newton, Halley, Cassini, and Flamsteed observed it carefully. Newton would use its parabolic path as evidence that the same inverse-square force ruled comets as planets, folding even these wild wanderers into the mathematical order of the Principia.