The Principia and comets

Abstract

Isaac Newton is one of the major luminaries in the history of cometary science. Before the publication of his Principia the following cometary problems were writ large: what was their physical and chemical form; what orbits did they have and why; and were they periodic or random ? New ton solved the second of these and published his solution in the Principia . His law of gravitation indicated that any conic section was a permissible orbit for any celestial body, comets included. The remarkable comet of 1680 was one of the keys to his discovery. Its orbit was found to be essentially parabolic and the Principia showed, for the first time, how its orbital parameters could be calculated. Principia can be regarded in part as a formidable textbook on comets and it contains a detailed discussion of the author’s views on these enigmatic objects. New ton discusses their planetary as opposed to stellar origins, their luminosity variation, tail formation, periodicity, mass, supposed influence on Earth, and role as a fuel for stars.