Yes, you read it right! just like a leap year, we had leap second on June 30th, 2015. June 30th ended the day with GMT 23:59:60 adding a second to Earth’s atomic time. NASA stated this has been done to sync up with the earth’s rotating speed as it’s gradually slowing down.
This was not the first time that a leap second was added to the world time. In fact, it started back in 1972 and this year was the 26th time that we have adjusted our time with Earth’s rotation. The last leap second was added on June 30, 2012. And it had many websites like Reddit, FourSquare, Gawker, StumbleUpon, LinkedIn, and Yelp to collapse. It also has contributed to delayed or cancelled flights. Google has been added up a fraction of a second from past few years so they don’t face sudden shifts of time.
By the year 2100 there would be a time difference of 2 to 3 minutes between Earth’s actual rotations to our atomic time if we didn’t add a leap second. There is not a periodic time regulation shift like leap year; it has to be performed whenever the time difference is 0.09 seconds.
Since January 1972, timekeeping has been maintained in accordance with the atomic time scale. The Earth is currently losing about three-thousandths of a second per day, and atomic clocks are just over six-tenths of a second fast on UTC right now. The addition of the leap second will keep the difference from exceeding nine-tenths of a second.
Leap seconds are inserted, when needed, either on June 30 or at the very end of the year, on Dec. 31.