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94 Scientific Advances
In the more-advanced and scientific approaches to comets, Tycho Brahe measured the parallax of a comet in 1577, which showed it was outside the atmosphere of the Earth. Isaac Newton derived his Law of Universal Gravitation, for which he showed the occasional parabolic orbits of objects. He was able to correlate a parabolic orbit to a comet in 1680.Edmund Halley applied Newton’s Law of Universal Gravitation to a series of comet appearances over some 350 years. Three of these comet appearances had similar orbits; Halley hypothesized it was the same comet. Based on this, Halley predicted the comet would return in 1758 or 1759; the comet did appear as Halley predicted and was named Halley’s Comet.
