This post initially appeared on Science Blogs
I rely on my phone to keep track of time - I tend to lose/break or cover watches in chalk, but my phone is pretty reliable. But how does it know the time, and how to people keep track of the passing seconds? Find out in this month's SITN Flash.
While atomic clocks are technologically more complicated than the average timepiece, their operating principle is more or less the same - time is kept by precisely measuring the frequency of a signal. Frequency expresses how often a periodic signal repeats itself. In a grandfather clock, the frequency refers to the number of times per second a pendulum swings back and forth as it mechanically drives the clock's hands; for a modern quartz watch, the frequency of interest is the number of electrically driven vibrations per second in a crystal, a signal that is converted into electronic pulses that are displayed digitally.
In contrast with conventional clocks, atomic clocks tune their ticks to the oscillations of atoms as they absorb particular frequencies of light. There's also some great history on the standardization of world times. Give it a read - you won't regret it.
[image by me from my trip to Bern, Switzerland in 2008]