Speaker: Christopher Ekstrom, Chief of Advanced Clock Development, U.S. Naval Observatory. September 27, 2012 (1:13:00)
Speaker: William Saturno, Assistant Professor of Archaeology at Boston University. October 22, 2012 (1:19:00)
Speaker: Dava Sobel on CSPAN-2 on March 5, 2014. (53 mins. Video from the LHL lecture is unavailable)