On April 19, 1610, upon receiving an advance copy of Galileo’s Starry Messenger, Johannes Kepler composed a fan letter. “I may perhaps seem rash in accepting your claims so readily with no support of my own experience,” Kepler wrote to Galileo. “But why should I not believe a most learned mathematician, whose very style attests the soundness of his judgement?” We are not accustomed today to thinking of a mathematician’s work in terms of style.