ABSTRACT
Sometimes all this talk about the definition of time-whether on the rotation of the Earth, the length of the year, or the vibrations of caesium atoms-seems remote from daily life. If you or I want to know the time we don’t observe the passage of stars with a transit telescope, we don’t take photographs of the Moon over several years to work out what Ephemeris Time was when we started, and we don’t take weighted averages of a couple of hundred atomic clocks around the world. We look at a clock.
