Tomorrow Time Stops for a Second

Why Time Will Stop For a Leap Second

Time will stop on June 30, but don't worry: It will only be for a second. Researchers will add a sliver of time—a leap second—to the world's clocks.

Just as leap years keep our calendars lined up with Earth's revolution around the sun, leap seconds adjust for Earth's rotation. This kind of fine-tuning wasn't much of an issue before the invention of atomic clocks, whose ticks are defined by the cycling of atoms. Cesium-based clocks, one kind of atomic clock, measure the passage of time much more precisely than those based on the rotation of our planet, so adding a leap second allows astronomical time to catch up to atomic time.

Atomic Clock

An atomic clock based on cesium ticks away at the German National Metrology Institute in northern Germany.

Most of us won't notice the addition, which happens at 23:59:59 coordinated universal time (UTC), or 7:59 p.m. ET, unless we deal in timescales shorter than a second, or if we use a computer program that crashes because it can't handle the leap second. It's happened before: The 2012 leap second brought down Reddit, Gawker Media, and Mozilla.

"It's a major interruption mostly because there are a lot of systems that aren't prepared to handle the leap second correctly," says Judah Levine, a physicist at the National Institute of Standards and Technology (NIST) in Boulder, Colorado. Leap seconds occur irregularly, which makes it hard for programmers to test their fixes, he explains.

Levine is responsible for making sure the nation's timekeepers at NIST can handle the leap second. When it comes time to adjust their clock, NIST will transmit 23:59:59 UTC twice, Levine says. "Once when that time arrives, and once again for the leap second."

So 6 p.m. mountain time—the NIST offices in Colorado are seven hours behind UTC—on June 30 will be stressful. "There's a full panic mode just before and after 6 p.m.," he says.

Even if all goes well during the addition, Levine and his team are usually greeted the morning after by a deluge of emails concerning various problems.

Not everyone recognizes the leap second, although Apple does so on its devices. Google mobile devices sync with internet time services that are usually tied to atomic clocks. But "if you have a standard Windows system, [it] just ignores the leap second," Levine says.

Financial markets like the New York Stock Exchange also take the leap second into account. The exchange will close the market a half hour earlier than normal, at 7:30 p.m. ET on June 30, to help their systems deal with the addition.

Courtesy: NGC

Tags: Leap Second, Atomic Clock, Earth, Clock