[size=150]three volume book, 1963[br][br][size=150][url=http://www.feynmanlectures.caltech.edu]www.feynmanlectures.caltech.edu[/url][br][/size][br][size=150][b]Numerical approach to the proof of Kepler's laws[/b][/size][br]Chapter 9: Newton's Laws of Dynamics, Section 9-7: Planetary motions[br] Feynman, R., Leighton, R. and Sands, M. The Feynman Lectures on Physics, 2[sup]nd[/sup] ed., Volume 1, Addison Wesley, USA, 2005. (pages from 9-6 to 9-9)[/size]