MIT Professor Emeritus Walter Lewin, famous for his astrophysics research as well as for his undergraduate physics lectures, retuned to the lecture hall on Thursday to deliver a public talk on the history of X-ray astronomy. He detailed major scientific breakthroughs from 1962 through 1972 that led to the discovery of X-ray-emitting objects throughout the galaxy. The lecture was part of “An Astronomical Event,” a day-long symposium presented by the MIT Department of Physics and the Kavli Institute for Astrophysics & Space Research.