Skip to main content

Who decides how long a second is? - John Kitching


5,403 Questions Answered

TEDEd Animation

Let’s Begin…

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.

Additional Resources for you to Explore

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!

More information about time in the US can be found here.

Next Section »

About TED-Ed Animations

TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator John Kitching
  • Director Tjoff Koong
  • Narrator Addison Anderson
  • Animator Tezo Kyungdon Lee, Magnus Lenneskog
  • Sound Designer Stephen LaRosa
  • Director of Production Gerta Xhelo
  • Editorial Director Alex Rosenthal
  • Producer Bethany Cutmore-Scott
  • Editorial Producer Dan Kwartler
  • Script Editor Alex Gendler
  • Fact-Checker Eden Girma

More from How Things Work