The International Telecommunication Union will decide this week not only whether there’ll be an extra leap second in June, but whether it will be the last of its kind. The decision could mean that we no longer take any notice of the Sun when it comes to determining time.
As we’ve previously covered, the leap second is necessitated by the way we currently measure time — simply observing the Earth’s movement round the Sun and dividing by the relevant fractions — which is inherently flawed. That’s because the Earth is slowly moving away from the Sun, thus increasing its orbit time.
While the leap year deals with the fact that the time of the orbit doesn’t precisely divide into 365 days, the leap second deals with the disparity between the solar second and the time measured on atomic clocks, which take the time from vibrations in cesium and thus aren’t affected by the slowing orbit time. That’s important as such clocks are ultimately used to inform most computer systems.
Each June 30th and December 31st, depending on the disparity, officials will have decided whether to add an artificial leap second to the atomic clocks. As a result the solar and atomic clocks are never more than a second out. (Unfortunately the leap second does occasionally cause systems to freak out, for example if they’ve been programmed with a calendar that didn’t anticipate the change.)
The International Earth Rotation and Reference Systems Service, which oversees atomic clocks, has concluded we’ll need a leap second in June, the first time in three and a half years. That should be formally approved this week by the ITU, which governs Coordinated Universal Time (UTC), the “what the atomic clock says plus leap seconds” system used by computers.
That same conference could also see a final decision on a long-standing proposal: that the ITU officially ditch leap seconds, ignore solar time, and let Coordinated Universal Time (UTC) simply match the atomic clock for the foreseeable future. The main argument for the change seems to be that every time we have a leap second (or even every June or December we don’t), it’s just another opportunity for somebody to miss the switch or make one when it isn’t needed.
The plan is that if the idea is adopted, the ITC would still keep track of and publish the disparities between atomic and solar time, even though it would be for information purposes only.
The ITC has also noted that left unchecked the disparity will hit the one hour mark in about 550 years, and critics have argued that within a few millennia we’d be left with dark “noons” and light “midnights.” The unspoken ITC position seems to be that this is a problem our descendants can sort out.