The U.S. Naval Observatory added an extra second to our nation's atomic clocks just before midnight on New Year's Eve to match up those global time standards with the earth’s rotation. It was the first "leap second" added since 1998, and the 23rd since an international timekeeping agreement was adopted in 1972. It says Coordinated Universal Time, an atomic time used as the world standard, can’t diverge from astronomical time by more than nine-tenths of a second.

Adjustments are necessary because modern atomic clocks are extremely accurate, while the planet’s rotation speed is affected by climate, tides and other natural factors – including tectonic shifts of the type that cause earthquakes, the circulation of molten rock inside the earth, ocean levels and the size of polar ice caps. In recent decades, the rotation speed has slowed very slightly. That means atomic clocks must be reset from time to time, so to speak, in order to match nature’s astronomical time.

Not all astronomers and physicists think this is a smart idea. There’s a scientific debate over whether it’s helpful or disruptive to tinker with time this way.

Critics say: There’s no urgent need to tweak time. They feel the leap second should be abolished because this random adjustment of time imposes unreasonable and perhaps dangerous disruptions on precision software applications used by cell phones, air traffic control and power grids.

Defenders insist: It would be expensive to adjust satellites, sophisticated telescopes and other ground systems that are hard-wired for the leap second every seven years. "The case (for change) hasn't been made," said astronomer Ken Seidelmann at the University of Virginia. "We've had (leap seconds) for 30-plus years and there's no outcry. I see no reason to get rid of them."

What’s the impact? Coordinated Universal Time signals from atomic clocks are critical in decisions about when and how to point solar panels or satellite image receivers. Clocks in computer operating systems also are synchronized automatically with the official time source.