Galileo was born in 1564, the same year as Shakespeare and Marlowe. By 1609, Marlowe was famous and seventeen years dead; Shakespeare had written all the major plays except The Tempest; Galileo had done nothing in particular. He had dabbled in literary criticism and many other genres, occupied an undemanding post as a professor of mathematics, and supported his relatives and hangers-on largely through a sideline making his “military compass.” This was a complex calculation device that, like modern software, cost for the package and cost again for the training. Besides that, Galileo’s intellectual capital consisted of some disorganized jottings on mechanics and an unshakable conviction of his own genius.

Then opportunity knocked, and Galileo was ready to move fast. Rumors reached Italy of a Dutch invention involving glass lenses in a tube that magnified objects at a distance. Galileo’s knowledge of geometry and experience in instrument-making came together. By the winter he had a version that magnified twenty times. On January 7, 1610 he turned the telescope on Jupiter. It had three unknown stars next to it, in itself not surprising as many new stars were evident. The next night, the tiny stars seemed to have got ahead of Jupiter instead of being left a little behind. January 9 was overcast. On January 10, the stars were still with Jupiter but in a different position. Galileo realized he had discovered moons, the first celestial discovery in recorded history (except for transient events like comets). A fast