The Clash Between William Herschel and the Great German ‘Amateur’ Astronomer Johann Schroeter

Abstract

A distinction will first be made between the terms ‘amateur’ and ‘professional’ astronomer in the late eighteenth and early nineteenth century. William Herschel, who began his career as a musician but became a salaried employee of the British Crown, clashed metaphorical swords for many years with Germany’s greatest amateur astronomer, Johann Schroeter. Each possessed the largest telescope in England and Germany, respectively. Schroeter began in the 1780s by purchasing telescopes made by Herschel, but his larger instruments were eventually made in Germany. Herschel began using his 20-foot telescope in 1783, but it would be another decade before Schroeter had a comparable instrument.

After briefly reviewing their correspondence from 1783 to 1804, their disagreements will be surveyed. These include very different measures of the diameter of Mars, and Herschel’s critique of Schroeter’s lunar, Venusian and Saturnian work. Their very different world views, as revealed by their telescopes, was the subject of a book by August Gelpke. Nowhere were these world views in starker juxtaposition than in their observations of and conclusions about Ceres and Pallas. They measured diameters in the same way, but came up with very different results. Schroeter also made a claim for a vast atmosphere around the objects, that caused variations in their light. These dual issues caused controversy and consternation among the entire astronomical community, and critiques from Carl Gauss, Wilhelm Olbers and Giuseppe Piazzi are noted. Schroeter’s rejoinder to the diameter measurement debate is also given. Finally, Herschel and Schroeter clashed about the very nature of Ceres and Pallas. The former named them ‘asteroids,’ but Schroeter explicitly stated that they were planets, not asteroids.