William Herschel and Comets

Abstract

The bulk of what historians have written about William Herschel deals with his ideas on the structure of the Milky Way, as well as on the nature of the nebulae and stellar clusters that he cataloged. His study of Solar System bodies has been particu- larly neglected, excepting of course his remarkable 1781 discovery of Uranus that permanently changed him from a musician to an astronomer. Yet fully 40% of Herschel’s publications in the Philosophical Transactions of the Royal Society (hereafter Phil. Trans.) were on Solar System topics. Is this corpus just a sideline, of little interest in understanding his grand schemes on the “Construction of the Heavens”? In this article we focus on only a fraction of Herschel’s Solar System research, that on comets, and argue that in fact it was importantly connected with his picture of a larger “sidereal universe.” Unlike his sister Caroline, William never discovered any new comets, but his acute observations of their structure with his superb telescopes, combined with his fertile mind, led to many new ideas.