Taking the Measure of Time

Throughout the ages, humankind's attempt to demarcate our days has resulted in a succession of breakthroughs, from sundials to wristwatches and atomic clocks

  • By Per Ola and Emily D'Aulaire
  • Smithsonian magazine, December 1999, Subscribe
 

Writers Per Ola and Emily d'Aulaire began their quest to trace the history of time at a legendary site — the Royal Observatory in Greenwich, England. Here, at the prime meridian, the imaginary line (demarcated by a plate-glass strip) that encircles the globe north-south, marking zero degrees longitude, crowds of visitors gather daily. These pilgrims stand at the very place where East meets West — and time begins.

Even those who can't journey to Greenwich can become time travelers here at home. A new permanent exhibition at the Smithsonian's National Museum of American History, "On Time," explores the changing ways Americans have measured, used and thought about the passage of days, hours and minutes during the past 300 years.

The d'Aulaires reach all the way back into prehistory, to a 30,000-year-old bone, discovered in the Dordogne region of France: the carved grooves in that artifact appear to demarcate the moon's travels over a period of months and represent an early attempt at lunar timekeeping. The writers range into the world of the Greeks and Egyptians and beyond, into 18th-century Britain, where the quest to establish longitude resulted in the first accurate timekeeping aboard ship. Ultimately, this technological breakthrough would usher in the age of exploration and of empire building.

Today, scientists have developed the spectacularly precise atomic clock, based on the oscillation frequency of the cesium atom. Within a few years an even more advanced atomic clock, one that achieves an accuracy of just one second lost in 313 million years, will be operational. Even so, scientists and historians alike can agree that, when it comes to defining time, the passage of our days is rooted in a certain kind of eternal mystery.


Writers Per Ola and Emily d'Aulaire began their quest to trace the history of time at a legendary site — the Royal Observatory in Greenwich, England. Here, at the prime meridian, the imaginary line (demarcated by a plate-glass strip) that encircles the globe north-south, marking zero degrees longitude, crowds of visitors gather daily. These pilgrims stand at the very place where East meets West — and time begins.

Even those who can't journey to Greenwich can become time travelers here at home. A new permanent exhibition at the Smithsonian's National Museum of American History, "On Time," explores the changing ways Americans have measured, used and thought about the passage of days, hours and minutes during the past 300 years.

The d'Aulaires reach all the way back into prehistory, to a 30,000-year-old bone, discovered in the Dordogne region of France: the carved grooves in that artifact appear to demarcate the moon's travels over a period of months and represent an early attempt at lunar timekeeping. The writers range into the world of the Greeks and Egyptians and beyond, into 18th-century Britain, where the quest to establish longitude resulted in the first accurate timekeeping aboard ship. Ultimately, this technological breakthrough would usher in the age of exploration and of empire building.

Today, scientists have developed the spectacularly precise atomic clock, based on the oscillation frequency of the cesium atom. Within a few years an even more advanced atomic clock, one that achieves an accuracy of just one second lost in 313 million years, will be operational. Even so, scientists and historians alike can agree that, when it comes to defining time, the passage of our days is rooted in a certain kind of eternal mystery.

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Comments (1)

Why does time add up from the bitrh of Christ and counts down to the birth of Christ. Such as AC__BC.

Posted by phil marshall on January 4,2009 | 07:34 PM



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