Measuring. We do it every day. We measure length, width and height. We measure mass and weight (weight being the effect that gravity has on mass). Lastly, we measure volume. But what about time?

Time can be measured using calendars; i.e. years, months, weeks, and days. The calendar is based upon celestial events. The year was originally based upon the Vernal Equinox, the month on the new moon, the week on the phase of the moon and the day the time from sundown to sundown.

The day is further broken into hours. The original hour was a time period based upon the movement of stars and it was decided that there were 12 of these units from sunset to sunrise. Since on the equinox, the night is roughly the same length as the day, there were also 12 units from sunrise to sunset…thus 24 hours in a day.

Five thousand years ago the hour was then further divided into 60 minutes using the sexagesimal system. The sexagesimal system is based upon 60 because 60 can be divided evenly into halves, thirds, fourths, fifths and of course, sixths. The base 60 can also be divided into 10 units, 12 units and 15 units.

The minute was then divided into seconds…again, 60 of them. However, accurately measuring something that small was a problem. You needed a timekeeper. The first clocks were sundials, and they gave you a rough idea what time of day it was. However, at night they were no good, and no good for measuring minutes, what’s more, seconds.

Water clocks were the first accurate clocks, and they date back to 1,600 BC. Water was poured into the top of the clock and gravity pulled the water through small openings into a series of catch pans that filled and emptied themselves. It works because gravity is constant and thus the interval we call time from putting the water into the clock and it coming out was always the same. Water clocks were accurate to about one second of time/day, however, they were large and required constant attention to maintain.

A similar instrument was an hourglass. Instead of water this instrument used sand flowing from one bulb into another. The hourglass was not as accurate as a water clock, but they were smaller and thus easier to transport and use. Magellan used 18 hourglasses on his ship during his trip around the world. Still, something better was needed.

In 1583 Galileo, after watching the action of a chandelier in Church, developed the physics behind the pendulum and speculated it could be used as a clock. Seventy-five years later Christian Huygens took Galileo’s physics of the pendulum and made a clock.

Pendulum clocks were so accurate there were no better timekeepers until 1937 with the development of the quartz watch. Quartz watches were accurate to one second in three years. In the 1950’s atomic clocks were developed that were based upon the vibration of cesium atoms. Today, the Master Atomic Clock at the U. S. Naval Academy sends a signal to a satellite in space, which then sends a signal to the clock on my wall. They tell me the Master Atomic Clock is accurate to within one second in 300 million years! What will come next?