June 30 to be Longer Than Usual Thanks to Leap Second

61-Second Minute Expected to Cause Some Computer Glitches

By Paul Riegler on 29 June 2015
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While the year 2015 may not be a leap year, it will have a leap second.

According to the National Aeronautics and Space Administration, or NASA, June 30 – this coming Tuesday – will be a little longer than usual because it will be the recipient of a leap second at 7:50:60 p.m. EDT (23:59:60 GMT).

“Earth’s rotation is gradually slowing down a bit, so leap seconds are a way to account for that,” said Daniel MacMillan, a principal scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a statement.

A typical day has 24 hours or 86,400 seconds.  However, because the Earth’s rotation is gradually slowing down a bit, the average length of a day based on how long it takes the Earth to rotate is actually 86,400.002 seconds.  While these extra two milliseconds are barely noticeable, they do add up.

Enter the leap second.

On any other day, the clock (in 24-hour time) would move from 23:59:59 to 00:00:00 the next day.  But since June 30 will have a leap second, i.e. a minute with 61 seconds, the clock will move from 23:59:59 to 23:59:60 before hitting 00:00:00 on July 1.

Leap seconds were first used in 1972 and, in the period ending 1999, there was one leap second occurring once a year on average.  Since 2000, there have only been four including this Tuesday’s.

Because leap seconds are not planned much in advance, they can create some issues and challenges for computer seconds.  Because of this, some experts have proposed abolishing the leap second, a topic that is expected to be considered later this year by the International Telecommunication Union.

A leap second in 2012 caused disruptions to the Amadeus airline reservation system for over two hours, impacting dozens of airlines, and it also caused disruptions for a number of popular websites including Gawker, LinkedIn, and Yelp.

Meanwhile, some companies aren’t taking any chances.  The leap second is scheduled to happen just as stock markets in Asia are opening. As a result, U.S. stock markets have announced plans to end some after-hours trading early and other markets are recalibrating their clocks in advance of the leap second.

(Photo: Accura Media Group)

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