Keeping the clocks on time

BBC News: Meet the world's director of time.

As 2008 turns to 2009 at the end of this month, an extra second will be added to every clock. But who decides exactly what time it is? Professor Brian Cox meets the man in charge of all our timekeeping - the world's director of time.  Time is something we all take for granted. Morning turns to evening; autumn drifts into winter and another year becomes history as the earth completes one more journey around the sun. But what is time? How do we measure its passing? Does it always tick at the same rate? Did it have a beginning, and will it ever end?

The rotation of the Earth is not an accurate marker for time, because it speeds up and slows down, partly because of wind blowing against mountains.  That boggles the mind!  They use measurements from distant galaxies, corrected for relativistic effects, to co-ordinate the GPS satellites and keep everyone on the same clock.