The rise and fall of the sun, the cycles of the moon and even the weather helped drive humans to understand the concept of time. From the sundial, to water clocks to the atomic clock, we have learned to keep time with ever increasing accuracy.

The earliest time keeping devices are thought to date back over five thousand years. Ancient timekeeping was based primarily on the movement of the sun and other celestial bodies. Various adaptations of what have become known as sun clocks relied on the predictable movement of the earth in relation to the sun. The ancient Greeks developed an early sun clock using an obelisk.

Similar in shape to the modern day Washington Monument the Greek obelisk tapered from the bottom to the top. The shadow cast by the obelisk would project onto a linear plane marked off in regular increments. The sun clock had one significant limitation in that it was not portable. Later developments like the sun dial would address the issue of size and portability. By the tenth century, the sundial had become portable, almost in design to a pocket watch.

The sun dial used the very same principle as the larger sun clock. The most significant change was the use of a round reference plane. A center post was oriented towards the east and the dial was marked in five increments. After the sun would reach its zenith, the clock would be turned one hundred and eighty degrees to indicate time during the afternoon. Two extra time periods or hours, were added to compensate for the early morning and early evening periods. The accuracy of shadow clocks and sundials was far from perfect but suitable for the times.

The next step in time telling was the development of various water clocks. From the Mediterranean to Asia, water clocks reflected attempts to use other methods of telling time without the use of the sun or other celestial bodies like planets and stars. The principle behind the water clock was simple. Water was placed in a vessel and water would drip from the vessel through a hole in the bottom. The process is very similar to the way sand moves through an hour glass, which would be developed centuries later.

The Chinese are credited with the invention of a mechanical clock that the movement of water as a power source. Using an escapement mechanism, the clock work would move series of rods and gears. Accuracy remained a problem since the flow of water was not easily controlled. Not until the thirteenth century did the mechanical clock become a useful time telling tool. Powered by opposing weights, early clock movements still lacked accuracy. The famous, and controversial Italian physicist Galileo Galilei, conceived the idea of using a swinging pendulum as a means of maintaining consistent movement of the clock works. Though the idea was developed in the early fifteen eighties, it would take over ninety years for the idea to be applied successfully.

Variations of the pendulum clock continued to be developed over the next three hundred years. Along the way, timepieces became portable with the development of spring powered clocks and pocket watches. Still, the pendulum clock remained the center of the timekeeping universe for many years. Early hanging wall clocks with their exposed movements were eventually replaced by cabinet clocks.

A cabinet clock is defined as any clock where the works, with the exception of the pendulum and weights was enclosed. Floor clocks, today referred to as grandfather clocks, became a staple piece of time telling equipment. Tall and ornately designed, floor clocks remain popular today. Floors clocks are interchangeably referred to as grandmother clocks, granddaughter clocks, tall case clocks and long case clocks.

Spring power led to the development of bracket and mantle clocks. Small enough to be portable, bracket and mantle clocks could often be found in areas of the home where people gathered most, whether on a table or a fireplace mantle. The were the precursors of the modern day tabletop clocks.

Floor clocks, though beautiful and timeless, eventually gave way to wall clocks. Today, the humble wall clock remains a standard timepiece in many homes, schools and businesses. Thousands of designs have been applied to the wall clock. Still popular are pendulum wall clocks. The complex movements of the pendulum clock have gradually given way to newer technologies.

Quartz crystal movements for clocks and watches have revolutionized timekeeping. Without moving parts, other than the hands, quartz crystal movements work the principle of using the piezoelectric properties of the crystal to produce a constant electrical signal. Quartz movements take a minimum of power to operate. Prior to the wide use of global satellite positioning systems, the accuracy of quartz clock movements was of particular importance to the maritime trades.

Navigating on the open sea was largely a function of keeping time. Some maritime clocks take advantage of radio signal technology. The clock is able to receive radio signals from a central, highly accurate atomic clock. Maritime clocks often have the capability to track the tides in certain parts of the world.

The atomic clock is by far the most accurate timekeeping system ever devised. First built in late nineteen forties, the atomic clock was accurate to within one second per years. Later designs were built using cesium isotopes that increased the accuracy to an astonishing thirty billionths of a second per year.

The humble clock has become a fixture of everyday life. Designers have been busy over the years developing stylish ways for us to keep time.