Roger Hahn presents a public talk at UC Berkeley on July 18, 2009, in celebration of the International Year of Astronomy, as part of the series described at astro.berkeley.edu/iya . Galileo revolutionized astronomy by turning his telescope to the heavens in 1609. The full story of his achievements is replete with complications that make it difficult for modern man to realize how troublesome his discoveries were in his own times. Many of them stem from Galileo’s personality which was calculated to upset the established order; others from the changes his pioneering work forced upon traditional astronomers, and more especially upon the Catholic Church. 400 years later we picture him as a critical link in the progress of our understanding; but in his own times he was soundly criticized and properly condemned.  Born in France, Roger Hahn, now retired as a Professor of History, has taught the history of science at Berkeley for the past 48 years, and is an expert on classical celestial mechanics of the solar system. His latest book was a biography of Pierre Simon Laplace whose work completed the Scientific Revolution Galileo helped to advance. More than many other past figures of significance, Galileo has been exclusively judged by modern standards. As a professional historian, Hahn is a strong believer in setting the past in its context. Seen in this perspective Galileo was a serious troublemaker. He deserved much of the reproach he encountered. Videography and editing by Chris Klein. This video is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License - creativecommons.org/licenses/by-nc-sa/3.0/us