Just as we add an extra day each Leap Year to account for the difference between our 365-day calendar and the actual time it takes Earth to revolve around the Sun, an occasional Leap Second is needed to keep the world’s clocks in sync with Earth’s rotation about its axis.
Eternal Clock. Robbert van der Steeg (Flickr)
The need for adjustment stems from the fact that the planet’s rotation is gradually slowing down, due primarily to tidal forces. But while the length of the solar day changes, our atomic clocks go right on ticking, oblivious to the fact that a day has become slightly longer.
Recently, the question has been raised as to whether keeping our timekeeping in sync with the solar day is worth the technical obstacles and cost to business and governments. With financial transactions, cellular phone networks, air traffic control, industrial and countless other applications dependent upon precise timing, the Leap Second adjustment of time is more involved — and the need for predictability more critical — than it once was.
Since 1988, the decision of when to add or subtract a Leap Second has fallen to the International Earth Rotation and Reference Systems Service (IERS), which releases a bulletin each January and June indicting whether a adjustment will be made six months hence. When adjustments are necessary, they are always made at midnight June 30 or December 31.
Some countries, including the U.S., Japan, Italy, Mexico and France have proposed abandoning the Leap Second, citing such difficulties as the inability of computer systems to precisely schedule processes beyond 6 months in the future, since an adjustment is always possible, but not predictable.
Other countries, including the UK, Canada, China and Germany, favor keeping the Leap Second; most nations, however, believe further study of the technical considerations and options is needed.
Unable to resolve the matter this week during a meeting of the ITU Radiocommunication Assembly, a decision has been postponed until 2015.
The most recent Leap Second was added at the end of December 31, 2008, and the next is scheduled to be added this June. In all, 25 Leap Seconds have been added since they were instituted in 1972. Never has second been subtracted.
Without adjustment, the difference between the solar day and our clocks would amount to about 30 minutes by the year 2700.
