Hope everyone enjoyed 2016, because this year is going to last one second longer than usual
स्रोत: News Bharati English      तारीख: 31-Dec-2016

Paris, December 31: If you’re counting the seconds until you can kick 2016 on high note, you’ll have to count a little higher to do so. According to our clocks, 2016 will be exactly one second longer this year because scientists are adding a leap second to it. This is done to keep our clocks in sync with the rotating Earth.
The International Earth Rotation and Reference Systems Service, or IERS, said it would be necessary to introduce a "leap second" at the end of December. Timekeepers use this added second much as leap years are used to bring the world's atomic clocks in sync with the Earth's own distinctive rhythm, which in this case is determined by its rotation.

On December 31, the world’s timekeepers will add in a “leap second” to keep all our clocks in sync with the Earth’s rotation. They do this because the Earth technically takes a bit longer than 24 hours to complete a full rotation of about 86,400.002 seconds. So a “leap second” gets added every few years.

How the time is measured?

Basically, we have lots of ways of measuring time. One is to very carefully measure how long it takes the Earth to spin once on its axis. We call that a “day.” The world keeps track of time in a bunch of different ways, many of them completely irrelevant to most people. We call that a “day.” There are actually lots of different kinds of days—how long it takes the Earth to spin.

Why the leap of second is added to 2016?

The Earth makes a pretty ratty clock when you focus in on very tiny timescales. Lots of forces affect our planet’s spin, including the tides from the Sun and Moon, continental drift, and even the way we dam up rivers. "Lots of people think the Earth's rotation is a simple, 24-hour thing," Steve Allen of the University of California's Lick Observatory said. "But weather in the atmosphere, in the ocean, and in the core of the Earth makes it complicated,” he added.

New standard defined a second as 1/86,400th of an average day — but that was based on the estimate of an average day in 1900. The problem is that days have generally been a bit longer since then, as the Earth’s rotation has slowed, and so a discrepancy has formed between solar time and official time. The difference is very small, amounting to less than a second per year. But if we didn't start using leap seconds to account for it, the two clocks would now be nearly 30 seconds apart. Eventually, over centuries, this could lead to the sun reaching the highest point in the sky minutes after official noon and over millennia, the gap could get hours long.

Hence on Saturday night, December 31, 2016, at 23:59:59, one second will be added to our clocks. Instead of clicking over to Jan. 1, 2017, at 00:00:00, for one second the official time clock will instead read 23:59:60.