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Don’t leap to change Coordinated Universal Time (UTC)

By: Astrodamus
The American Astronautical Society just published “Decoupling Civil Timekeeping from Earth Rotation,” a book on the future of Coordinated Universal Time (UTC), the foundation for almost all clocks around the world. The book details the proceedings of a colloquium held at AGI in October 2011 at which prominent specialists and authorities on timekeeping met to discuss the implications of redefining UTC. In essence, this means doing away with periodic adjustments known as leap seconds that keep clocks in sync with the Earth’s rotation. An assembly of the International Telecommunication Union will vote on the issue at a meeting scheduled for Jan. 16-20, 2012, in Geneva. There was general agreement at the AGI colloquium that there is not sufficient information to support the need for a change and a decision to change should be deferred until impacts on economics, religion, law, historical record, science and engineering can be identified and planned for. The science behind the issue is that the Earth’s rotation speeds up and slows down by a few milliseconds per day with daily, seasonal and longer cadences. In addition, the average length of the day has increased by a few milliseconds per century because of tides caused by the Moon.  Over thousands of days, these small variations accumulate and require adjustments to keep civil time synchronized with the actual rotation of the Earth, so-called leap seconds, every few years to the time kept by atomic clocks. If the proposal to cease making these adjustments is accepted, the many millions of clocks worldwide – whether on computers, phones or wrists – would no longer be tied to the rotation of the Earth or the passage of the Sun through the sky. This is an unprecedented proposal and would be a remarkable philosophical shift in humanity’s relationship to our planet.  “Decoupling Civil Timekeeping From Earth Rotation,” which is Volume 113 of the Science and Technology Series, goes into the issue in great detail. It was edited by AGI’s John H. Seago, as well as Robert L. Seaman, National Optical Astronomy Observatory and Steven L. Allen, UCO/Lick Observatory. Contributors include Dr. Neil deGrasse Tyson of the Hayden Planetarium, Dr. George H. Kaplan of the International Astronomical Union, Dr. Daniel Gambis of International Earth Orientation Center in Paris, Danny Hillis of the Long Now Foundation and Applied Minds, LLC, and experts from the Vatican Observatory, NASA and astrophysical observatories worldwide. The book can be purchased from Univelt. Preprints of the articles, transcribed discussions and original presentations are available at  Of particular interest are the results of a survey of more than 400 professionals—with more than 76% preferring that UTC not be changed.
Posted: 1/5/2012 5:49:13 PM