If the name Edmund Halley sounds vaguely familiar, you have likely heard of the comet whose trajectory was calculated first by him. A scientist by trade, Halley took up studies at Oxford, where a chance encounter with the astronomer John Flamsteed encouraged him to pursue a cataloging of stars seen from the Southern Hemisphere. Halley developed a great interest in the sky, but could not come up with an adequate mechanism explaining the celestial body movements. He traveled to consult with Isaac Newton, another eminent physicist and astronomer of the day, and discovered to his amazement Newton already solved it.

On this day, December 19, in 1684, Edmund Halley presented Isaac Newton’s findings to the Royal Society in London, the foremost scientific body of Britain of the age.

Newton was at first reluctant to publish his treatise at all, and relented only after great encouragement from Halley and a promise to assume all the printing costs. The published work, Philosophiae Naturalis Principia Mathematica, released in 1687, revolutionized the field of astronomy. Newton’s calculations are still widely used today, more than three centuries later.