David J. Helfand has served on the Columbia University faculty for forty-six years, nearly half that time as Chair of the Department of Astronomy. He has mentored 22 PhD students in projects ranging from supernova remnants and neutron stars to the cosmic X-ray background and in various areas of radio astronomy. Most of his pedagogical efforts have been aimed at teaching science to non-science majors in 2004, Columbia’s 250th year, he finally succeeded in implementing a vision he began working on in 1982 that has all Columbia first-year students taking his science course as part of the University’s famed Core Curriculum. He received the University’s 2001 Presidential Teaching Award and the 2002 Great Teacher Award from the Society of Columbia Graduates. In 2005, he became involved in the effort to create Canada’s first independent, non-profit university, Quest University Canada. He was a Visiting Tutor in the University’s inaugural semester and served as President & Vice-Chancellor from the Fall of 2008 through 2015. From 2011-2014, Prof. Helfand served as President of the American Astronomical Society and was named a Society Legacy Fellow in 2020. He is currently Chair of the Board of the American Institute of Physics. His first book, “A Survival Guide to the Misinformation Age”, provides essential tools any informed citizen must have to combat the tsunami of mis- and dis-information threatening to drown all rational approaches to personal decision-making and the formation of good public policy. His second book, “The Universal Timekeepers” is the subject of this class.