Before the Transit of Mercury: forgotten forerunners of an astronomical revolution | Karl Galle

A manuscript note in the Royal Society Library hints at an observing program that would eventually transform our ability to predict the motions of the planets.

"Today I saw Mercury." This terse remark scrawled inside a 16th-century almanac could reflect anyone watching today's transit of Mercury across the Sun. The winding path this observation took after it was recorded, however, traces a century-long story leading through the transformation of both our understanding of the cosmos and the practice of astronomy itself.

Mercury's observer in this case was Willibald Pirckheimer, a German humanist who made diary notes in a set of astronomical tables by Johannes Regiomontanus, which are now preserved in the Royal Society Library. Pirckheimer almost certainly wasn't alone, as the same Mercury sighting (early in the evening of 18 March 1504) was recorded in more detail by his friend Bernhard Walther, who had inherited Regiomontanus' observation program and copious manuscripts. Perhaps it was solely an observing session, or perhaps it preceded one of the festive banquets Nuremberg's humanists were known for. We may not know the evening's full itinerary, but it's a reminder that science was rarely a solo activity even back then.