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What did Isaac Newton tell Edmond Halley about the shape of planetary orbits?
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Edmond Halley
Edmond Halley, detail of an oil painting by Richard Phillips, c. 1720; in the National Portrait Gallery, London.
When Edmond Halley visited Isaac Newton in 1684 to discuss the mechanical explanation for planetary motion, Newton informed him that he had already solved the problem: the orbit of a planet would be an ellipse.
Although Newton had previously worked out the proof, he told Halley that he had mislaid his calculations. Encouraged by Halley, Newton expanded his studies on celestial mechanics, which eventually led to the publication of his masterpiece, the Principia.1