2015 is not a leap year, but it does have a leap second, set to take place Tuesday (June 30) at 7:59:60 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," Daniel MacMillan of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. Ask any person the length of a day, and she'll say 24 hours, which equates to 86,400 seconds. But the time it takes for Earth to rotate on its axis relative to the sun, called a mean solar day (or the average length of a day) is roughly 86,400.002 seconds. This happens because Earth's rotation is slowing down, thanks to a kind of braking force caused by the gravitational tug of war among Earth, the sun and the moon, researchers at NASA said.
The astronomers at the International Earth Rotation and Reference Systems Service keep track of the difference between astronomical time and atomic time. They call for a leap second to be added whenever Earth's observed position is on track to be out of sync with UTC time by more than 0.9 of a second. Leap seconds traditionally are added on June 30 or Dec. 31. Because they are unpredictable, leap seconds can cause headaches for tech companies who cannot build them into their code the way they do with leap years. In the past, LinkedIn, Google and Reddit have all experienced problems caused by leap seconds. In addition, it is not clear that leap seconds are really essential. Even if the difference in astronomical time and atomic time grew by one second every year, in 100 years the gap would be less than two minutes. In 1,000 years, it would be off by less than 17 minutes. But it could be unsettling. Eventually. And besides, couldn't we all use a little more time?
