some of the common hits in kepler applet
http://www.ioncmaste.ca/homepage/resources/web_resources/CSA_Astro9/files/multimedia/unit4/keplers_laws/keplers_laws.html#[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=1501.0;attach=1939;image[/img]

http://www.surendranath.org/Applets/Dynamics/Kepler/Kepler3Applet.html[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=1501.0;attach=1941;image[/img]

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=9[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=1501.0;attach=1943;image[/img]

http://astro.unl.edu/naap/pos/animations/kepler.swf[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=1501.0;attach=1945;image[/img]
Like: a lot! that is a lot to learn more.