The Sidereal Messenger

In the winter of 1609 and 1610, Galileo turned a telescope of his own making on the night sky and rushed into print within weeks. The little book that resulted reports mountains and craters on a Moon that was supposed to be a flawless sphere, hundreds of stars invisible to the naked eye crowding the Milky Way, and four small bodies circling Jupiter, which he named the Medicean Stars to flatter his Florentine patrons. It was the first scientific work built on telescopic evidence, and its plain drawings did more damage to the old cosmology than any argument had. This edition adds part of Kepler’s preface to the Dioptrics, an early and generous response from a fellow astronomer. Free to download as a PDF or EPUB.