[size=150]In 1964 Feynman gave [size=150][size=150]a guest lecture [i]The Motion of Planets around the Sun[/i][/size] to the Caltech freshman class[/size], the aim of which was to present a geometric proof of the elliptical motion of planets around the Sun.  [/size][br][size=150][br]Inspired by Newton’s geometric way of proving Kepler's laws of planetary motion, which is presented in [i]Principia[/i] (1687), Feynman derived his own geometric proof based only on elementary knowledge of plane geometry combined with the selected statements of Newton's laws of motion and gravity. [br][br]Owing to the temporary disappearance of records of this lecture it became known as [i]Feynman’s Lost Lecture[/i]. After finding it among other documents from the Physics Department of Caltech it was published in a book [i]Feynman's Lost Lecture, The Motion of Planets around the Sun[/i] by D. L. Goodstein and J. R Goodstein in 1996.[/size]