17th December

On this day in 1610 Father Christoph Clavius SJ, the senior mathematician at the Collegio Romano wrote to inform Galileo that he and other Jesuits at the college had seen the four moons of Jupiter. Only two months earlier he had said that if Galileo saw "planets" around Jupiter in his glass, then he must have put them there.

On this day in 2012 Google released a Chatelet doodle.