Walter Lewin’s halo revealed

Walter Lewin's ring picture

A couple months ago, MIT physics professor Walter Lewin posted a photo of an MIT construction site to the Astronomy Picture of the Day webpage with the challenge “explain the bright ring of colors.” Now after answering about 3000 answers (only 5 of them fully correct), Walter Lewin explains all.

(Note also that 75 of Prof. Lewin’s lectures are available online at MIT’s OpenCourseWare site, plus four more at MIT World).