Leap Second: 2015 Will Be One Second Longer — Extra Second To Be Added On June 30

Internet, software and computer engineers are preparing themselves for problems they could face with their systems after the International Earth Rotation and Reference Systems (IERS) announced earlier in the year that an extra second — a leap second — will be added to clocks on June 30 to account for the difference between solar time measured by the Earth’s rotation and time measured by atomic clocks.

The extra second will be added at midnight coordinated universal time (UTC), 8 p.m. EDT in the U.S.

What this means is that the year 2015 will be longer by a second.

There are fears that computer systems and software not equipped to accommodate the adjustment could have issues. The problem is similar to the so-called Y2K bug challenge at the beginning of the century due to transition from a system in which the year was abbreviated to two digits to one in which the year was represented with four digits (“2000”).

Experts say that the need for a leap second adjustment arises because the Earth’s rotation is gradually slowing down by about two-thousandths of a second every year compared with atomic clocks which keep constant and accurate time.

On June 30, the leap second adjustment to coordinated universal time (UTC) means that atomic clocks will go from 23:59:59 to 23:59:60, instead of to 00:00:00. The procedure means effectively that clocks pause for a second before finally going to 00:00:00.

The one-second pause is to allow the Earth’s rotation to catch up with atomic time.
Already, computer software and Internet companies are bracing themselves for the problems that their systems could develop when a leap second is added. The last time a leap second was added in June 2012, several Internet software and websites, such as Mozilla, LinkedIn, Reddit and Stumbleupon experienced problems.

The Network Time Protocol (NTP) that many computing systems use is designed to keep time with atomic clocks and not with the Earth’s rotation. They are also not designed to accommodate adjustments involving adding an extra second due to the slowing down of the Earth’s rotation.

But some Internet companies have devised their own solutions to the problem.

Atomic Clock
Atomic Clock FOCS-1, One Of The Most Accurate Clocks In The World

Google, for instance, had come up with a special procedure it calls the “leap smear,” which involves breaking up the extra second into milliseconds and spreading the millisecond bits over a period of time so that by the time the extra second is being added officially, Google’s time-keeping system has already accounted for it.

ABC News reports that Amazon Web Services announced it will “implement alternative solutions to avoid the leap second. This is interpreted to mean that AWS clocks will read time different from the adjusted standard civil time briefly.

According to the IERS, leap seconds can be added in June or December. The first time that a leap second was added was in 1972. According to The Telegraph, at least one leap second was added every year from 1972 to 1979. A leap second was added six times in the 1980s. There have been four leap seconds added since 1999.

Atomic Clock
Master Atomic Clock Ensemble Of The US At The US Naval Observatory.

The extra leap second to be added on June 30 will be the 26th time a leap second has been added.

The need to add a leap second arose only after the second was redefined in 1967 with reference to radiation cycles in the cesium 133 atom. Greenwich Mean Time (GMT) was the basis of universal time until 1967 when the second was redefined and coordinated universal time (UTC) adopted.

Royal Observatory
Shepherd Gate Clock At The Royal Observatory, Greenwhich

Unlike UTC, which is kept using accurate atomic clocks, GMT was measured as solar time based on astronomical observations. Greenwich Mean Time, first adopted in 1847, is measured by observing the moment the Sun crosses the Greenwich Meridian. Thus, clocks were adjusted regularly to correspond with the rotation of the Earth which tends to slow down — but may occasionally speed up — due to the interaction between Earth and the moon, such as in tidal drag and other natural phenomena, including earthquakes.

However, some experts are dissatisfied with the current system in which UTC is kept by adding leap seconds to reconcile solar time and time measured by atomic clocks.

The U.S. is reportedly considering abandoning the practice altogether. Some experts say the practice disrupts precision systems used for navigation, communication, and in the global financial system for timed money transactions.

However, the U.K. has defended the practice of adding a leap second to reconcile solar time and time measured by atomic clocks, saying that it is essential to maintain the link between measurement of time and the natural cycle of rising and setting of the sun because our concept of time has over the ages become intimately linked with the Earth’s rotation, the basis of the solar day.

But some critics allege that Britain’s support for the system is due to the desire to perpetuate the Greenwich Mean Time system.

Other experts argue that it is risky to experiment with breaking the link between our measurement of time and the natural cycle of day and night due because once leap second adjustments are discontinued it will be impossible to revert to it after leap seconds have accumulated into minutes or hours.

[Images: Wikimedia Commons]