Johannes Kepler (1571–1630)

I just read this in the first edition, 1610, at the Houghton Library, Harvard. I was looking up Kepler's four references to Giordano Bruno, two in his Introduction (essentially half the 76pp) and two in the work itself. In the Intro Kepler mentions Bruno and Pythagoras together as positing other worlds--in relation to Galileo's observing "new worlds," the moons of Jupiter which he "sells" to the Florentine Medici as a worthy memorial, more worthy than a statue. Galileo calls the four moons he sees (out of 63 now identified) the "Medici Stars."
Kepler considers, what Bruno asserted, the possible inhabitation of the Moon. Kepler has a telescope, which Bruno never did. On the basis of observing the lunar surface, Kepler says, "If men live on the Moon, they must live in caves (speluncas), because their day is fifteen times as long as ours."… (more)