Edmond Halley's Magnificent Prediction

Edmond Halley's Magnificent Prediction

English astronomer and mathematician Edmond Halley was the first to predict the return of a comet.

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English astronomer and mathematician Edmond Halley became the first to calculate the orbit of a comet, arguably the most famous of all comets today, named Comet Halley in his honor. He was also friends with Isaac Newton and contributed to Newton's development of the theory of gravity, which helped establish our modern era of science, in part by removing all doubt that we live on a planet orbiting around a sun.

But, in Edmond Halley's time, people didn't know that comets were like planets in being bound in orbit by the sun. They didn't know that some comets, like Comet Halley, return over and over. Comets were thought to pass only once through our solar system. In the year 1704, Halley had become a professor of geometry at Oxford University. The following year, he published A Synopsis of the Astronomy of Comets. The book contains the parabolic orbits of 24 comets observed from 1337 to 1698.

It's also in this book that Halley remarks on three comets that appeared in 1531, 1607, and 1682. He used Isaac Newton's theories of gravitation and planetary motions to compute the orbits of these comets, finding remarkable similarities in their orbits. Then Halley made a leap and made what was, at that time, a stunning prediction. He said these three comets must in fact be a single comet, which returns periodically every 76 years.

He then predicted the comet would return, saying:
Hence I dare venture to foretell, that it will return again in the year 1758.

Halley didn't live to see his prediction verified. It was 16 years after his death that – right on schedule, in 1758 – the comet did return. The scientific world – and the public – were amazed.

It was the first comet ever predicted to return. It's now called Comet Halley, in honor of Edmond Halley.

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