The American GPS system is currently revolutionising the way we navigate. Once a secretive Cold War military weapon it now adorns the dashboards of one in three cars.
But GPS is much more than a handy navigational tool. The constellation of 24 satellites each contain some of the world’s most accurate chronometers in the shape of atomic clocks. These provide such accuracy in timing that a million years could pass and not even a second would have been gained or lost
These clocks are what enable us to pinpoint our location on Earth as a GPS receiver can workout how long the timing signal took to reach it and therefore how far away from the satellite it is. Using three or four satellites means an exact location can be pin-pointed by triangulation. Atomic clocks need to be used as just one seconds inaccuracy could mean a location could be hundreds of thousands of miles out because of the vast distances radio signals can travel in that time.
These timing signals can also be utilised to provide extremely accurate synchronisation for computer networks by receiving the timing signal via a GPS antenna connected to a GPS time server. A GPS time server uses NTP (Network Time Protocol) to synchronise machines on a network.
Because of the accuracy of the atomic clocks a GPS Time Server can obtain an accuracy to within a few hundred nanoseconds of UTC time (a nano is one billionth of a second)
UTC (Coordinated Universal Time) is a global timescale developed after the invention of the atomic clock. It is a standardised time scale base on Greenwich Meantime but allows for the minute slowing of the Earth’s rotation (caused by the Moon’s gravity).
A GPS time server can also receive a timing signal from anywhere in the world (as long as it can get a clear view of the sky)