The most accurate clock in the world is redefining the second

By Jen Christensen, CNN

Updated 1731 GMT (0131 HKT) May 25, 2016

Researchers have created this atomic clock using the atoms of the element ytterbium at the National Institute of Standards and Technology in Boulder, Colorado. They say it could be the most precise method of measuring time in the world. Click through to explore other clocks that are important in other ways.
Photos: Keeping time
Researchers have created this atomic clock using the atoms of the element ytterbium at the National Institute of Standards and Technology in Boulder, Colorado. They say it could be the most precise method of measuring time in the world. Click through to explore other clocks that are important in other ways.
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Caral, the oldest ancient city of South America, located in Peru, includes this sundial. The city is thought to be nearly 5,000 years old.
Photos: Keeping time
Caral, the oldest ancient city of South America, located in Peru, includes this sundial. The city is thought to be nearly 5,000 years old.
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The Zytglogge clock tower in Bern, Switzerland, dates to the early 13th century and the clock itself to 1530.
Photos: Keeping time
The Zytglogge clock tower in Bern, Switzerland, dates to the early 13th century and the clock itself to 1530.
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True, the name "Big Ben" refers to the 13-ton bell inside, but honestly, what image says "London" quite like the famous clock and tower?
Photos: Keeping time
True, the name "Big Ben" refers to the 13-ton bell inside, but honestly, what image says "London" quite like the famous clock and tower?
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This antique is the Tiffany clock at Grand Central Terminal in New York. Each day, 700,000 people pass through the terminal, which opened in 1913.<br />
Photos: Keeping time
This antique is the Tiffany clock at Grand Central Terminal in New York. Each day, 700,000 people pass through the terminal, which opened in 1913.
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A million people cheered in Times Square in New York on December 31, 2012, as the clock moved toward midnight and the traditional crystal ball dropped.