The pre-telescopic observations of the Moon in early seventeenth-century London: The case of Edward Gresham (1565-1613).

This article supplements the history of the pre-telescopic observations of the Moon at the turn of the seventeenth century with an analysis of the hitherto understudied manuscript Astrostereon or the Discourse of the Falling of the Planet (1603), written by Edward Gresham, an English astrologer and follower of the heliocentric theory. In this treatise, Gresham presents the results of his observations of the surface of the Moon. These findings are discussed against a wider background of contemporary writings by Galileo Galilei, William Gilbert, Johannes Kepler and Michael Maestlin. Furthermore, Gresham's studies of the Moon are shown as part of London astronomical pursuits represented by Gilbert, the author of the first map of the Moon made on the basis of naked-eye observations (c.1600), and by Thomas Harriot, who outran Galileo in telescopic observations of the Moon (1609). It is suggested that Gresham's reports may have helped Harriot to select the time of his first observation of the Moon and therefore determined its result.