According to the US Naval Observatory, 31, December 2016 would be a second longer than other years as a “leap second” would be added to the world’s clocks at 23 hours, 59 minutes and 59 seconds.
This would be an additional added second to the Coordinated Universal Time (UTC) and thus would make the year 2016 a second longer than other years.
People would thus have to wait an extra second to welcome the new year 2017 and officially start it.
UTC is computed in Paris at the International Bureau of Weights and Measures (BIPM) and they have decided to add an additional second this year as the Earth on an average revolves slower by about 1.5 to 2 milliseconds per day than the atomic time and after some time this difference increases to a full second.
At the above rate, the BIPM Scientists have determined that this second, which is added after roughly 500 to 750 days, would be added on December 31, 2016.
Historically the time was calculated on the mean rotation of the Earth, and the second was defined in this reference frame. Now since the invention of atomic clocks, the calculation is much more precise.
To calculate the difference between the two time scales, the International Earth Rotation and Reference Systems Service (IERS) has been set up and it’s them who have calculated the date to be December 31 when this difference of a second, which is called a leap second, would be inserted.
The new system was instituted in 1972, and at that time it was found that the difference between International Atomic Time and UTC was 10 seconds.