Posted by Daniel Waldron on March 9th, 2015
The Paris Observatory has announced an additional leap second will be added to clocks in June 2015. What does this mean for businesses? Galleon Systems examines.
According to the Paris Observatory, an extra leap second is required this summer so that atomic time can synchronise with the Earth’s rotation, which is gradually slowing down.
Software companies in particular are now preparing themselves for glitches following the announcement.
From June 30th, dials will show 11:59:60 as clocks pause for a second, this means that on that day there will be 86,401 seconds rather than 86,400, giving the Earth’s rotation a chance to catch up with atomic time.
While atomic time is constant, the Earth’s rotation is experiencing a slow-down in speed, currently two thousandths of a second per day, according to a report published in the Telegraph.
International Earth Rotation Service
Responsibility for monitoring the Earth’s rotation, for the purpose of fine-tuning time, lies with the International Earth Rotation Service (IERS) located in France.
It’s closely monitored because some years the Earth’s rotation matches time and no changes are required.
However, the IERS has spotted a slight slow-down in rotation recently, hence the need for an additional leap second.
NASA asserts that millions of years ago, roughly around the time of the dinosaurs, Earth completed a rotation in 23 hours.
By 1820, a rotation took exactly 24 hours and this has since increased by 2.5 milliseconds year-on-year.
The need for leap seconds
Leap seconds are required to measure two sources of time – one which uses the vibration of atoms, which is known as Coordinated Universal Time (UTC) and one which uses the Earth’s rotational spin (UT1).
The rotational average of the Earth was utilised to track time until use of the atomic clock was implemented in 1970, supplying a much more accurate measure.
A day based on Earth’s rotation actually lasts a fraction longer compared with the atomic clock’s measurement.
The IERS calls for leap seconds to be added to keep the difference between the two time measurements within 0.9 seconds of each other.
The US Naval Observatory commented: “We can easily alter the time of an atomic clock, but it’s obviously impossible to adjust the Earth’s rotational speed to match the atomic clock.”
Problems for businesses
The last time a leap second was added, in 2012, Foursquare, LinkedIn, Mozilla, Reddit, StumbleUpon and Yelp all reported seismic crashes.
There were also issues with the Linux operating system and programmes written in Java.
The bigger issue is that the majority of computer systems rely on Network Time Protocol (NTP) and Network Time Servers to maintain accurate time, using the world’s atomic clocks.
However, the majority of systems and devices are not programmed to manage an unexpected extra second.
A history of leap seconds
In 1972, the first leap second was added to clocks and this will be the 26th addition.
This means the rotation of the Earth has slowed by 26 seconds when compared with the time measurement of atomic clocks.
Between 1972 and 1979, at least one second was added for every year. Across the 1980s, six additional leap seconds occurred.
However, since 1999 just four leap seconds have been added, with the US Naval Observatory stating that ‘they are becoming rarer.’
Abolishing the leap second
The US is in favour of eliminating leap seconds, deeming them to be too disruptive to precision systems used for navigational and communicational purposes.
During a conference in Geneva in 2012, US delegates argued that ‘precision timed monetary transactions could go wrong and vehicles could be led astray by tens of metres if time measurement is inaccurate by a second.’
Britain on the other hand rejects the idea of abolishing leap seconds, claiming that it would ‘sabotage the link between our concept of time and the rising and the setting of the Sun.’
It would also signify the end of Greenwich Mean Time (GMT), which is measured by the time at which the Sun crosses the Greenwich Meridian.
GMT became the standard time measurement in the UK in 1847.
Abolition being considered
In a statement from the Curator of Horology at the Royal Observatory Greenwich, Roy McEvoy, he said: “Since ancient times the Earth’s rotational spin has supplied us with our timescale. It gives us the most basic unit of time, the ‘solar day’.
During the early 20th century, GMT was distributed via radio signals.
The clocks connected to radio transmitters were constantly checked and altered, when required, according to astronomical determination of time.
This method did not require leap seconds. Not until the SI second was redefined in 1967 did leap seconds become an issue, because time was now based on atomic timekeeping.
At this stage it was decided that Coordinated Universal Time (UTC) should correlate with the Earth’s rotational spin.
In 1972 the first leap second occurred, applied to UTC, to correct the discrepancy between the two.
While the Earth’s rotation has a propensity to slow down – predominantly impacted by the relationship between Earth and the Moon – it can also speed up.
Therefore, it’s possible that a negative leap second could be added to UTC.
The fact is though, the abolition of the leap second is being given serious consideration and, with close to 12 years of discussion, it’s likely that a decision will be made this year.”
How do NTP servers deal with leap seconds?
NTP servers can implement leap seconds by repeating the final second of the day.
GPS NTP Servers in particular are extremely useful for avoiding leap second disruption.
By utilising GPS time, system administrators can make their own provisions to adjust for leap seconds.
This prevents administrators being caught off-guard by automatic adjustments to UTC time sources, over which they have no control.
The ntpd process on Linux should be able to pre-empt leap seconds, preparing devices on the network 24 hours prior to changes.
Additionally, some devices will make minor adjustments during the day, giving the appearance that 60 seconds has elapsed. Other devices will simply alter the time by a second once a leap second occurs.