Who decides how long a second is?

Discover how scientists developed atomic clocks, which use the vibrations of atoms to measure and maintain a globally consistent time.

In 1967, researchers gathered to answer a long-running scientific question: just how long is a second? It might seem obvious at first. A second is the tick of a clock, the swing of a pendulum, the time it takes to count to one. But how precise are those measurements? And what is that length based on? John Kitching digs into how we scientifically define this fundamental unit of time.

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The way we measure time has changed throughout history and it is continuing to evolve. Currently, the Gregorian calendar is used globally to measure days, weeks, and months. However, the Gregory calendar wasn’t the first solar calendar. Before it, the Julian calendar was used and it replaced previously used lunar calendars such as the Roman calendar. Lunar calendars are still used by communities to this day.

Did you know that many people around the world use atomic time daily? Watch this TED-Ed Lesson to learn how the GPS in your smartphone uses atomic time. You can also check the time whenever you want on the internet here.

The international definition of time, and other units, is organized by the Bureau International des Poids et Mesures (BIPM) in Sevres, France. There is also a Superhero Measurement League!

Lesson by John Kitching, directed by Tjoff Koong.

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