The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States, with a primary mission[1] to produce Positioning, Navigation and Timing (PNT)[2] for the United States Navy and the United States Department of Defense. Located in Northwest Washington, D.C. at the Northwestern end of Embassy Row, it is one of the pre-1900 astronomical observatories located in an urban area; at the time of its construction, it was far from the light pollution thrown off by the (then-smaller) city center. Former USNO director Gernot M. R. Winkler initiated the "Master Clock" service that the USNO still operates,[3] and which provides precise time to the GPS satellite constellation run by the United States Air Force. The USNO performs radio VLBI-based positions of quasars with numerous global collaborators, in order to produce Earth Orientation parameters.