Tomorrow, July 20, 2019, will mark the 50th anniversary of the landing of Apollo 11 on the moon: the module of the spacecraft called _Eagle_ settled on the _Sea of Tranquility_, a relatively smooth, basalt area of its surface. The poetic name Mare Tranquilitatis was coined by two astonomers: the first was the 17th-century scientist and astronomer Francesco Grimaldi, who drew a map of the moon (this style of map has its own name: -selenograph), shown on the second image. The other scientist, Giovanni Battista Riccioli, named many craters and mountains on the moon, and it is the frontspiece of his _Almagestum novum_ (1651), that you see posted here. The _New Almagest_ shows the muse of astronomy weighing competing visions of the solar system: the heliocentric model of Copernicus against his own geocentric vision (both are better than the old model of Ptolemy’s, which is cast off below).
