Halley, Edmond

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Halley, Edmond (1656–1742) English astronomer and mathematician, astronomer royal (1720–42). His most famous discovery (1696) was that comets have periodic orbits. In 1705, he accurately predicted the return (1758) of the comet now known as Halley's comet. Halley founded modern geophysics, charting variations in Earth's magnetic field and establishing the magnetic origin of the aurora borealis. He showed that atmospheric pressure decreases with altitude. Halley financed Isaac Newton to write Principia (1687).

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