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The Country’s Most Accurate Atomic Clock is in Boulder

It loses just one second every 300 million years.


If your Timex runs a few minutes slow, the worst thing that might happen is that you miss your bus. If just one of Xcel Energy’s power plants lags behind official United States time, however, a city could face a rolling blackout. That’s why generating stations sync with the country’s most accurate atomic clock—housed on the Boulder campus of the National Institute of Standards and Technology (NIST). NIST’s latest atomic timekeeper (there have been seven previous iterations) will lose just one second every 300 million years. It keeps such precise time by tuning its microwave frequency (aka electromagnetic radiation) to the rate required for cesium atoms’ electrons to change energy levels. If you don’t have a Ph.D. in quantum physics, don’t worry. All you really need to know is that the frequency it takes to rattle those subatomic particles (9,192,631,770 hertz) determines our most basic unit of time: a second. In addition to monitoring waves of energy, NIST keeps us all in sync by disseminating the current time through various methods. One involves sending out a signal through the Fort Collins radio station WWVB, so radio-controlled clocks can automatically reset themselves when we move to daylight saving time on March 11. Of course, your cell phone, which gets its time via GPS signals, automatically resets at 2 a.m. local time, too, so you’ll need another excuse for being late to that morning meeting.

This article appeared in the March 2018 issue of 5280.

Mary Clare Fischer, Assistant Editor

Mary Clare Fischer co-edits 5280’s Compass, Adventure, and Culture sections; writes for multiple sections of the magazine; and blogs weekly about health and wellness for 5280.com.

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