Retrograde loops

Retrograde loops

. This photograph shows the apparent movements of the planets against the background stars. Mars, Jupiter and Saturn appear to stop in their orbits, then reverse direction before continuing on a phenomenon called retrograde motion by modern astronomers. Ancient and modern explanations for this temporary backward motion are illustrated in Figures 1.6 and 1.9, respectively. (Courtesy of Erich Lessing/Magnum).

Copyright 2010, Professor Kenneth R. Lang, Tufts University