Everyday Time and Atomic Time: Part One

NIST/JILA Fellow Judah Levine discusses the history of time and frequency measurements

View as a Web Page Taking Measure Blog Everyday Time and Atomic Time: Part One Coordinated Universal Time (UTC) is the legal time in most countries. Currently, UTC is based on data from an international ensemble of atomic clocks combined with astronomical observations on the rotation rate of Earth. The UTC time scale is kept within 1 second of astronomical time (which I will define later) by the occasional addition of "leap seconds." Several current proposals suggest changing the way UTC is computed, either by making the addition of a leap second much less frequent or by discontinuing the process of adding leap seconds altogether. In this series of essays, I will explain how the UTC time scale was defined, why leap seconds are needed, and why there is a discussion to eliminate them. Read More IN CASE YOU MISSED IT Keeping Time at NIST June 23, 2020 Einstein is reported to have once said that time is what a clock measures. Some say that what we experience as time is really our experience of the phenomenon of entropy, the second law of thermodynamics. Entropy, loosely explained, is the tendency for things to become disorganized. Hot coffee always goes cold. It never reheats itself. Eggs don't unscramble themselves. Your room gets messy and you have to expend energy to clean it, until it gets messy again. Here at NIST, we don't worry about any of these philosophical notions of time. For us, time is the interval between two events.  Read More

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