Introduction

The GPS system is a practical example of the application of Relativity. Both effects of Special Relativity and General Relativity need to be taken into account. The Special Relativity aspect corrects for the fact that the satellite clocks are moving rather fast with respect to a ground based receiver. The General Relativity aspect corrects for the fact that the satellite clocks are in a different gravitational field. If these effects were not taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and in general errors in global positions would accumulate at a rate of about 10 kilometers each day!

Figure 17: The GPS Satellite system