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What Time Is It When the Clock Shows 23:59:60?

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Jun 29, 2015
This article is part of a series called News & Trends.

Get ready for Leap Second day.

What’s that, you ask? It’s the day that, if you’re quick about it, you might see your cell phone display 23:59:60.

Didn’t catch that? Take a closer look. It’s not a time that clocks ever show. We go from 59 seconds to the next minute in the sequence. But with the Earth slowing down, every once in a while the world’s timekeepers add a second to our official time. Tuesday is that day.

Some of us might use that extra second for one more situp or a couple more steps on the treadmill or to Tweet a greeting at precisely 23:59:60 UTC to see what happens. The rest of will go about our day as always. Unless, as some worry, the extra second messes with the world’s computers. (You PeopleSoft users might want to check with your IT department about this.)

Financial markets globally are taking no chances. Bloomberg says some U.S. markets are ending after-hours trading early to avoid risking calamity should the computers that control transactions balk when their clocks try to digest the extra second that will added at 8 p.m. EDT. Markets in Asia that will be opening right about that time intend to set their clocks back before the official instance.

Don’t think the whole thing is a big deal? Consider this: Bloomberg says that in one second, 1.4 million order messages are sent; $4.6 million worth of stocks are traded, and; $3.7 billion worth of stocks change hands at the opening on exchanges in Korea, Australia, and Japan.

In 2012, the last time the International Earth Rotation and Reference Systems Service added a second, Internet services like LinkedIn, Yelp, Gawker, and others crashed or had hiccups. One of the bigger hiccups forced Quantas to delay flights for hours. And that was when the extra second was added over a weekend.

In the last few months, tech sites have been abuzz with worried conversations about the effect of the extra second on computer networks and especially on that ubiquitous programming language Java. A quick look at Slashdot or Stack Overflow finds no shortage of fixes. Oracle, heavily dependent on Java for its software, has blogged about the impact and what IT professionals should consider.

There’s great debate about how to adjust network clocks. There’s the all-at-once method in which computer clocks will read (in UTC time) 23:59:60, an otherwise impossible time. Another is to count the last second twice. And there’s Google’s “smear” method, spreading the second in small increments throughout today until the full second is accounted for.

Some think the entire matter is overblown, a leap second version of last century’s Y2K hysteria.

However, the U.S. Naval Observatory, timekeeper for the military, which includes the nation’s GPS system, and therefore, our cell phones and other navigation systems, estimates that 10 percent of the big networks may be affected to some degree. So as you do that extra situp, keep your eye on the clock and your Internet connection.

This article is part of a series called News & Trends.
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