# Time a relative matter in 2015

Most measures of time are absolute. A day is always 24 hours.  An hour is always sixty minutes. A minute is always sixty seconds. And a second is always 10 deciseconds, and so on.

But a year, oh what a tricky thing that seems to be. Though typically made up of 365 days, we all are aware of the leap year. Like the Olympics, it comes around every four years, and makes up for the problem that a revolution around the sun last roughly 365 days and six hours. This has been in place since the Gregorian calendar came to be in 1582.

But this manual modification of our calendar doesn’t end there. Because a day is slightly less than 365 days and six hours, the Gregorian calendar makes another adjustment. The standard leap year rule results in an error of three extra days per 400 years. To correct this, the calendar then omits the leap year in century years that are not divisible by 400. For example, despite the fact that 1896 and 1904 were leap years, 1900 was not.  The year 2000, being divisible by 400, was.

You might think that even-numbered years divisible by four have all the fun, but you’d be wrong. In fact, we are in store for some calendar adjustment fun this year. The International Earth Rotation and Reference System Service (IERS) in Paris, France has announced that this year they will add a leap second. Adjusting for daylight savings time, the extra second will be added at 6:59:59 p.m. here in Illinois on Tuesday, June 30. This corresponds to 11:59:59 p.m. in Coordinated Universal Time.

The issue stems from the fact that the rotation of the Earth on its axis is slowing. The IERS monitors the difference between the rotation of our planet and International Atomic Time. When the disparity grows to 0.9 seconds, the leap second is added.

While not even the most-rigidly scheduled person will notice this additional bit of time, our computer friends will. When computer systems approach conclusion of the 60th second of the 60th minute of that fateful hour, they will either calculate that second again or calculate a 61th second for that minute. Either way, computers could struggle to make sense of all of this. When the last leap second was added in 2012, companies such as Reddit, LinkedIn, Gizmodo, and FourSquare experienced CPU trouble. The leap second is registered by CPUs as system error, resulting in overload. GPS systems in planes and other vehicles could be affected as well.

Google, of course, has identified a way to fix this and stave off disaster after a 2005 leap second resulted in some of their systems not accepting new commands (though their advice was not heeded by others in 2012). Google adds milliseconds throughout the day that a leap second is to occur, which allows them to modify the systems without resulting in the major headaches that the one full second creates.

While there is some fuss over the pesky leap second, ultimately nothing should come of it. Those who manage computer systems will eventually devise strategies to deal with it, whether it be now or sometime in the future.

There is a silver lining to this little annoyance. I think we can all take some pride in the fact that while computers are now manufacturing goods more efficiently, driving cars more safely than us, and may one day rise up to enslave us, our computer overlords will still need us to help them adjust their watches.