Wolfram Demonstrations Projecthttp://demonstrations.wolfram.com/An Open Resource of Interactive Mathematica VisualizationsCopyright 2009 Wolfram Demonstrations Project & ContributorsEmpty Focus Approximation to Kepler's Second Lawhttp://demonstrations.wolfram.com/EmptyFocusApproximationToKeplersSecondLaw/]]>http://demonstrations.wolfram.com/EmptyFocusApproximationToKeplersSecondLaw/