Page "Halley's Comet" Paragraph 5

In 1687, Sir Isaac Newton published his Principia, in which he outlined his laws of gravity and motion.

His work on comets was decidedly incomplete.

Although he had suspected that two comets that had appeared in succession in 1680 and 1681 were the same comet before and after passing behind the Sun ( he was later found to be correct ; see Newton's Comet ), he was unable to completely reconcile comets into his model.

Ultimately, it was Newton's friend, editor and publisher, Edmond Halley who, in his 1705 Synopsis of the Astronomy of Comets, used Newton's new laws to calculate the gravitational effects of Jupiter and Saturn on cometary orbits.

This calculation enabled him, after examining historical records, to determine that the orbital elements of a second comet which had appeared in 1682, were nearly the same as those of two comets which had appeared in 1531 ( observed by Petrus Apianus ) and 1607 ( observed by Johannes Kepler ).

Halley thus concluded that all three comets were in fact the same object returning every 76 years, a period that has since been amended to every 75 – 76 years.

After a rough estimate of the perturbations the comet would sustain from the gravitational attraction of the planets, he predicted its return for 1758.