Timeline
Let's take a trip through time, from the epoch when farmers told time by looking at the sun to today, when atoms tell us the time.

Sundial

1500- 1300 BC

Sundial first used in Egypt to measure the time of day by the sun's shadow. Hours are shorter in winter and longer in summer

water clock

400 BC

Greeks use a water clock, which measures the outflow of water from a vessel, to measure time

Burning candles

980?

Alfred the Great (a Saxon king) uses burning candles to measure time.

1000? (Sung dynasty) Candles and burning incense mark time in China.

Mechanical clocks

1400s

 Mechanical clocks are built in Europe, using a mainspring and balance wheel.

Pendulum clock

1657 

1583 Galileo Galilei realizes that the frequency of a pendulum's swing depends on its length.

Christiaan Huygens invents the first pendulum clock, capable of far greater accuracy than any preceding timekeeper. But the clock does not work at sea.

Greenwich time 1884

Twenty- five countries accept Greenwich, England, as the prime meridian (0 degrees longitude). The prime meridian gradually becomes the basis for time throughout the world. Liberia finally adopts it in 1972.

Quartz clock

1928

 

 W.A. Marrison of Bell Laboratories builds the first quartz clock, accurate to within 1- 2 thousandths of a second per day. Quartz technology is later adapted for use in wristwatches.

Atomic clock

1949

The National Bureau of Standards (now the National Institute of Standards and Technology, or NIST) builds the first atomic clock, using ammonia.