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Welcome to 2012—a leap year. The additional day in a leap year keeps the calendar in sync with the seasons. They're needed because Earth rotates more like 365-and-a-quarter times in one lap around the sun.
In fact, Earth's rotation isn't all that reliable. It fluctuates a bit from year to year, and it's gradually slowing down thanks to the braking effects of lunar tides.
So the world's timekeepers occasionally add leap seconds to what’s called coordinated universal time, or UTC. Leap seconds keep UTC synchronized with the rotation of the Earth and with the positions of celestial bodies. Two dozen leap seconds have been tacked on to UTC since the 1970s.
But that practice may soon end. This month the International Telecommunication Union will consider a proposal to abolish leap seconds. Without them, the argument goes, the world's clocks could tick along continuously without the need for ad hoc adjustments.
The downside is that UTC would no longer describe Earth's orientation with respect to the sun and other stars. By 2050 the clocks would differ from the true celestial time about by about 30 seconds. And for stargazers, that’s an astronomical difference.
—John Matson
[The above text is a transcript of this podcast.]
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5 Comments
Add CommentA meeting in October resulted in 400 pages of analysis of this proposal. The documents are available through http://futureofutc.org/
Reply | Report Abuse | Link to thisI cannot believe that ITU is responsible for leap seconds or similar issues. See here, e.g., (http://www.huffingtonpost.com/2011/12/27/world-time-utc-clock-change_n_1171617.html):
Reply | Report Abuse | Link to this"But what scientists at the International Bureau of Weights and Measures in Paris, France (BIPM) have been considering eliminating next month could fundamentally change the way we tell time, and most people don't even know it exists. They plan on deciding whether or not to eliminate "leap seconds" from Coordinated Universal Time (UTC)."
Regards,
Hans Leander
Cleveland, Ohio, USA
The recommendation specifying that radio broadcast time signals should have leap seconds is http://www.itu.int/rec/R-REC-TF.460-6-200202-I/en and the draft of the new form is http://www.ucolick.org/~sla/leapsecs/draftTF460-7.html
Reply | Report Abuse | Link to thisSome time in the late seventies I stayed up late to listen to the leap second on WWV, thus proving to my wife that I was indeed a total nerd.
Reply | Report Abuse | Link to thisThe UTC second is an arbitrary unit that was defined so that it is slightly shorter than the ephemeris time second. That way, leap seconds are sometimes added but never subtracted. The mean drift between the UTC and ephemeris time scales can be minimized simply by redefining the UTC second. That predicted 30 second difference between the two time scales can be pretty much done away with by such a redefinition.
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