Time and Its Measurement in the New Millenium
Robert A. Nelson
President, Satellite Engineering Research Corporation
Friday, March 17, 2000 at 8:15 P.M.
The measurement of time is central to advanced engineering and communication systems. The precision
of time dissemination is now at the nanosecond level and is expected to reach a picosecond within a decade. The
history of clocks will be summarized, various time scales will be described, and the origin of the leap second
will be discussed. The effects of the special and general theories of relativity on time transfer algorithms are
significant in modern timekeeping systems and their magnitudes will be illustrated. The Global Positioning System
is a significant universal source of time. Its principles of measurement will be given and its current status and
future growth will be discussed.
About the Author:
Robert A Nelson is president of Satellite Engineering Research Corporation, an engineering consulting
firm in Bethesda, Maryland. Mr. Nelson holds the degree of Ph.D. in physics from the University of Maryland and is
a licensed Professional Engineer. He is also a lecturer in the Department of Aerospace Engineering at the University
of Maryland. Mr. Nelson is co-author of the textbook Satellite Communication Systems Engineering (Prentice-Hall, 1993)
and is Technical Editor of Via Satellite magazine. His publications include a variety of technical papers and
reports on the application of relativity to high precision time transfer systems.
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