The Johns Hopkins University Applied Physics Laboratory: This is the home page of APL. Access to all official publications and department news is accessed through a left hand vertical navigation bar. The APL Space Department is found at civspace.jhuapl.edu and milspace.jhuapl.edu. The JHUAPL Time and Frequency laboratory is presented at http://civspace.jhuapl.edu/facilities/tf_lab.php

IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society: This is the official site of the IEEE society devoted to the science and advancement of frequency control. The site contains an excellent on-line archive of past publications. IEEE member registration is required along with specific UFFC certification.

United States Naval Observatory: The official site of the Naval observatory features catalogues of astronomical observations a description of various sponsored science experiments and an animated GIF of the UTC clock.

MTP at JPL:  This is the main page for the Mars Technology Program at the Jet Propulsion Laboratory.  This program is dedicated toward development of the technology required to hasten NASA's "Mars Exploration Vision"  JPL is a significant sponsor for USO development, including the Synthesized USO referenced under R&D.