Galileo Galilei: Starry Messenger

Published in 1610 in Venice, Galileo Galilei’s Sidereus nuncius, or Starry Messenger, reported the fascinating discoveries that Galileo had made thanks to his telescope observations. It was the first published astronomical treatise to be based on direct telescope observation. Galileo had been interested in astronomy for a few years when, in 1609, he began to work to build his own telescope. This new instrument enabled him to make detailed observations of the moon, the stars in the Milky Way, and Jupiter’s moons. Galileo’s observations of the Moon allowed him to conclude that its topography was not too different from that of the earth. This conclusion challenged one of the basic principles of traditional Thomistic and Aristotelian cosmology, according to which celestial bodies were different on a quality level from the earth. Because of this challenge, the Starry Messenger caused some controversy. Yet, in 1611, the Jesuit Collegio Romano, the scientific authority of the Church, announced its support for all of Galileo’s discoveries—thus contributing to the establishment of his scientific reputation. It was also enthusiastically received by the German mathematician and astronomer Johannes Kepler.