WORT 89.9FM Madison · Farewell To The Leap Second

Human beings have an obsession with regularity.  We like neat squares, right angles and intervals of time that are precisely the same, no matter when or where we measure them.  Natural and astronomical phenomena, however, do not care about our preferences.  Take the rotation of the earth… we like to think that it rotates once every 24 hours, with an hour made up of 60 minutes and a minute made up of 60 seconds. In truth, though, the earth’s rotation on its axis is quite erratic – sometimes slowing down, sometimes speeding up.  That discrepancy between counted time and apparent solar time has caused meteorologists, astronomers and computer engineers fits.  Since 1972, the International Bureau of Weights and Measures, known by its French acronym the BIPM, has compensated for this discrepancy by introducing a “leap second” at midnight, Universal Time Coordinated occasionally when the difference becomes too great.  This week, the BIPM voted to ditch the leap second and just ignore the difference between apparent and counted time.  Judah Levine is a Professor Adjoint of Physics at the University of Colorado Boulder and the Chair of the International Bureau of Weights and Measures Committee on GPS and GLONASS Time Transfer Standards.

To convert from UTC time (without the “leap second”) to apparent solar time, see:

* International Earth Rotation and Reference Systems Service Bulletin A (latest version).

Photo of crescent earth from Apollo 4, NASA.

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