Galileo, Kepler share IYA anniversary

Abstract

Here’s a little postscript to the International Year of Astronomy 2009. Although it celebrated the 400th anniversary of the telescopic discoveries of Galileo, the IYA was the quadricentennial of another monumental event in the history of astronomy and physics—the publication of Johannes Kepler’s Astronomia Nova. In that work Kepler stated his first two laws of planetary motion: the ellipticity of planetary orbits, which finally broke the circular mindset of his predecessors, and the sweeping of equal areas in equal times (conservation of angular momentum). Surely his text deserves celebration as well, for it led directly to Newton’s law of universal gravitation later in that century.© 2010 American Institute of Physics.