On June 30 this year, an extra second called a leap second will be added to the Coordinated Universal Time (UTC). In other words, the said day will be 1 second longer than the usual 86400 seconds. This will be the 26th time since 1972 that scientists make the change in accordance with the mean solar day. The last mentioned term stands for the amount of time the Earth takes to rotate.
The Earth’s rotation is slowing down because of the gravitational influence of the Sun and the Moon. Apparently, the mean solar day has been 2 milliseconds longer than the average 86400 seconds since the year 1820. A millisecond accounts for a thousandth of a second. Over time, these small additions to the standard length of a day accumulate to reach a whole second. So on June 30, the International Earth Rotation and Reference Systems (IERS) will inject an extra second into the day just before the clock hits midnight.
In the highly accurate atomic time by which our daily lives move forward, 1 second is based on electromagnetic transitions in the atoms of the element cesium. A leap second is normally added to the day on June 30 or December 31, with the clock moving from 23:59:59 to 23:59:60, and then welcoming the next day at precisely 00:00:00, explains NASA. There are two ways to measure time; one being Very Long Baseline Interferometry (VLBI) for calculating how long the Earth needs to finish a full rotation.
It makes for the standard we know as Universal Time 1 (UT1). The other method takes cues from atomic time of course, and this is what is referred to as UTC. Since UT1 and UTC must be kept within 0.9 seconds of each other, it is necessary to reduce the difference between them by shoehorning a leap second into the equation. Between 1972 and 1999, an extra second was injected almost once a year. But the frequency has changed since then and only 3 needed to be added from 2000 till today.
Scientist haven’t been able to fully explain this phenomenon. A lot of factors affect the duration of a day on the Earth. Climate, shifts in the tectonic plates, groundwater, volcanic eruptions, tidal upheavals and so on have an impact on the speed of the Earth’s rotation. A good example is the 8.9-magnitude earthquake in Japan which occurred in March 2011. It is said to have shortened the 24-hour day by 1.8 microseconds. The slowing down or acceleration of our planet’s rotation cannot be predicted properly.
A lot of organizations want to abandon the practice of sticking an extra second to a day. But such proposals await the ruling of the International Telecommunication Union that’s expected to come later this year. Stretching the civil time also presents some problems in IT. Errors while applying time stamps is just one such issue. Google solves this by implementing a leap smear to extend seconds very slightly through the day until it syncs to the extended time.