The Dutch telescope and the Italian scientist Galileo have long enjoyed a durable connection in the popular mind--so much so that it seems this simple glass instrument transformed a rather modest middle-aged scholar into the bold icon of the Copernican Revolution. And yet the extraordinary speed with which the telescope changed the course of Galileo's life and early modern astronomy obscures the astronomer's own curiously delayed encounter with the instrument. This book considers the lapse between the telescope's creation in The Hague in 1608 and Galileo's alleged acquaintance with...

Galileo s telescopic discoveries, and especially his observation of sunspots, caused great debate in an age when the heavens were thought to be perfect and unchanging. Christoph Scheiner, a Jesuit mathematician, argued that sunspots were planets or moons crossing in front of the Sun. Galileo, on the other hand, countered that the spots were on or near the surface of the Sun itself, and he supported his position with a series of meticulous observations and mathematical demonstrations that eventually convinced even his rival.

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"On Sunspots "collects the correspondence that constituted...