Clocks - From the Sundial to the Ntp Server

Time is concept that has preoccupied the thoughts of humans since the earliest civilisations. It may only have been in the last century that we have begun to understand time, thanks to the work of Albert Einstein, but measuring its passing has been an important part of society.

Historically time has been measured using the Earth's rotation and other astronomical cycles such as the phases of the moon. The measuring of time and therefore identifying key events during the day, month or year has been essential for the development of farming, religion and sophisticated societies.

Whilst calendars have been around for millennia, from prehistoric monuments like Stone Henge, thought to indicate the winter and summer solstice and therefore identifying the longest and shortest of days for crop planting, measuring smaller increments of time has proven a technological challenge.

The first clocks were nothing more than timers, using water, burning tapers and sand. These were successful for measuring a set period of time but less useful in identifying how long left until daylight expired or other important events.

The sundial was the first real clock in that it was possible (on a sunny day) to divide the day into equal increments and thus provide a consistent measure of the day.

Mechanical clocks first appeared during the fourteenth century. Whilst their technology was based on simple mechanics and they were less accurate than existing sundials, they did provide a solution to the obvious drawbacks of the sundial (cloudy days).

Mechanical clocks really came into their own once the pendulum was developed in the 1600's which ensured the existing mechanical clocks could provide better accuracy. The development of mechanical, pendulum driven clocks rocketed throughout the next few centuries and they became increasingly accurate.

However, once it was discovered that certain crystals oscillate at exact rates whilst under the influence of an electronic current, electronic clocks soon took over as people realised they provided far better accuracy.

However, during the 1950's the atomic clock was developed, these used the oscillation of a single atom (normally caesium) that oscillated at an exact rate each second. Thanks to atomic clocks it was soon discovered that the traditional way of using the Earth’s rotation and other astronomical bodies as a basis of time keeping would soon cause problems as the Earth, it was discovered, would slow down or speed up in its rotation due to the effects of the Moon's gravity.

If nothing was done, then the time told by atomic clocks (International Atomic Time- TAI) would eventually run out of synchronisation with the Earth and night would slowly become day.

A solution was found in UTC (Coordinated Universal Time) where leap seconds were added to compensate for this slowing of the Earth's rotation.

UTC and atomic clocks have made possible technologies such as satellites, global communication and the Internet. Most computer networks are governed by an atomic clock via a NTP server (Network Time Protocol). NTP servers receive the time signal from an atomic clock from either a radio signal or the USA's GPS (Global Positioning System) network. This allows computers from across the globe to be synchronised to the same timescale (UTC) allowing time sensitive transactions such as the stock exchange and Internet trading.