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.
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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.]
