Astronomy recently celebrated the 400th anniversary of Galileo’s first observations with a telescope.  His discoveries, including four moons of Jupiter, were published in a sensational treatise, Sidereus Nuncius (The Sidereal Messenger), in 1610. German astronomer Johannes Kepler received a copy of the Sidereal Messenger in early April that year.  His response, the ‘Conversation with the Sidereal Messenger’, was completed and sent to Galileo on 19th – 400 years ago next month. A slightly revised version was published on May 3. In it, Kepler made the first observation of extraterrestrial artificial structures – circular fortresses on the moon!  Galileo had remarked upon these features, but it was left to Kepler to argue that because of their geometrical perfection, they must be artificial. … Read entire article »