Time controllers have (leap) second thoughts

One of the geekiest moments of any year, the leap second, may be under threat. The International Telecommunications Union, the organization that governs global communications issues including how computers deal with time, is calling for feedback on the idea of dropping the practice.

The leap second is designed to correct the disparity between the rigid consistency of an atomic clock (used for most automated timing systems, including computing) and the solar clock, which measures the movements of the Earth in relation with the Sun (hence giving us days and years).

Until 1967, the “official” definition of time was simply based on the Earth’s movements around the Sun: once round was a year, and a second was simply the appropriate fraction, depending on whether it was a leap year. The problem is that this period is slowly increasing as the Earth slips further away from the Sun.

The solution is the leap second: each year a leap second can be added on June 30 or December 31 (or both, or neither) to catch up the difference. Where this happens, the official measure of time, UTC, adds an extra second at the end of the relevant day. The idea is that the time we use, and the “true” solar time are never out of kilter by more than a second.

The reason for the proposed abolition is that the extra second can cause problems for computers using UTC. That’s because, unlike simply consulting a calendar for future dates, it’s not usually possible to predict when a leap second will be needed more than about six months in advance as their use depends on the actual, unpredictable, movements of the Earth. If you’re programming an application that depends on precise timings, you’ll need to build it in a way to keep it up to date.

The ITU proposal is to abandon the leap second, let the two times grow apart and perhaps chuck in a leap hour every couple of thousand years or so.

Critics of the proposal say that it would do more harm than good as most programmers who are affected by the time disparity have already tweaked their systems to take advantage of it and would be disrupted even further by undoing things.

[Picture credit: Screenshot of time.gov by Flickr user Jay Knight]


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