[Sci-all-l] Physics/Astronomy Colloquium: the effecs of Relativity on GPS

[Eric Myers]

                   Physics and Astronomy Colloquium
                   ================================
		       Monday, April 19th 2004
                          
		  "The Effects of General Relativity
		   on the Global Positioning System"

			      Eric Myers
			   (Vassar College)

                   Physics Lecture Hall (Room 207)
                      Sanders Physics Laboratory
                            Vassar College

          Tea and Cookies at 3:45, Lecture begins at 4:00 PM

The Global Positioning System (GPS) is based on a constallation of
satellites which carry atomic clocks in nearly circular orbits.
Anyone with an inexpensive receiver can use the GPS to obtain their
precise location in space (and time).

The basic principle behind the GPS is simple.  It uses the time of
flight of radio signals from multiple satellites to "triangulate" the
receiver's position in space-time.  However, the GPS would not
function correctly unless the effects of Einstein's General Theory of
Relativity (GR) are properly accounted for.  (They are!)

In this talk I will give a description of the GPS and show how it is
affected by relativity.  I will also discuss the famous "twins
paradox" in relativity.  I will explain why time really does run a
little slower in the south (how long is a New York minute measured in
southern seconds?)  and why UTC (Universal Time, Coordinated) is not so
"universal" after all.