Today, June 30th is Special - it has 86401 seconds - the leap second extra !!

A day has 24 hours – each hour has 60 minutes – each minute has 60 seconds – after 23:59:59 everyday, another day starts  - but today 30^th June  after 23:59:59 instead of  00:00:00, the time becomes 23:59:60 – sound illogical ? – heard of a leap second ?? – and it is not new ???  2015 is not a leap year, but it does have a leap second, set to take place Tuesday (June 30) at 7:59:60 p.m. EDT (23:59:60 GMT).  Ask any person the length of a day, and she'll say 24 hours, which equates to 86,400 seconds. But the time it takes for Earth to rotate on its axis relative to the sun, called a mean solar day (or the average length of a day) is roughly 86,400.002 seconds. This happens because Earth's rotation is slowing down, thanks to a kind of braking force caused by the gravitational tug of war among Earth, the sun and the moon, researchers at NASA said.

                   In The Age of Miracles, Karen Thompson Walker’s debut novel, the Earth apparently hasn’t received the same memo as most of its citizens: Instead of moving at a pace faster than ever, the planet’s rotation begins to slow. At first, the days grow by about 56 minutes. Eventually, each rotation takes longer than 48 hours. The novel explores scientific and environmental implications of “the slowing,” while focusing primarily on changes in society, relationships, and humanity itself.  Walker describes the lengthening days in such realistic detail—professional baseball games are thwarted by gravity’s changes; agriculture must rely on artificial light—Could this actually happen?  -  In fact, the  Earth’s rotation is slowing. But not at a rate that anyone would notice—unless one happens to be around in 150 million years.

Leap year we know – it is the year containing one additional day  in order to keep the calendar year synchronized with the astronomical or seasonal year. Because seasons and astronomical events do not repeat in a whole number of days, calendars that have the same number of days in each year, over time, drift with respect to the event that the year is supposed to track. By inserting (or intercalating) an additional day or month into the year, the drift can be corrected. A year that is not a leap year is called a common year.  In the Gregorian calendar, each leap year lasts 366 days instead of the usual 365, by extending February to 29 days rather than the common 28 days.

Since 1967, when clocks went atomic, human timekeeping has been independent of the earth’s rotation. The problem is, the planet is slowing down and clocks are not. So every few years, to get everything back in sync, scientists add a second. They’ve done it 25 times since 1972. The last time was 2012, but that was on a weekend. June 30 will be the first leap second during trading hours since markets went electronic.

The "leap second" means the last minute of June will have 61 seconds in it.  Leap seconds - and leap years - are added as basic ways to keep the clock in sync with the Earth and its seasons. However, there are concerns the extra second could cause problems for some computer systems because it has to be added manually. Will that cause any calculable harm as perceived in Y2K and would that send Insurers in a spot of bother ?  NASA has explained that June 30, 2015 will officially be a bit longer than usual because an extra second or "leap" second will be added. 

Daniel MacMillan of NASA's Goddard Space Flight Center in Greenbelt said that Earth's rotation is gradually slowing down a bit, so leap seconds are a way to account for that. A day lasts 86,400 seconds. That is the case, according to the time standard that people use in their daily lives, Coordinated Universal Time (UTC). UTC is "atomic time," the duration of one second is based on extremely predictable electromagnetic transitions in atoms of cesium. These transitions are so reliable that the cesium clock is accurate to one second in 1,400,000 years. However, the mean solar day, the average length of a day, based on how long it takes Earth to rotate, is about 86,400.002 seconds long. Scientists estimate that the mean solar day hasn't been 86,400 seconds long since the year 1820 or so.

"Earth's rotation is gradually slowing down a bit, so leap seconds are a way to account for that," Daniel MacMillan of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. Because of these planetary forces, a mean solar day likely hasn't lasted 86,400 seconds since about 1820, NASA scientists said.  Two milliseconds might not sound like much, but it adds up to almost a second over the course of a year. However, in reality, it's much more complicated. Earth's rotation may be gradually slowing down, but individual days can also vary in unpredictable ways, the researchers said.  Many factors can affect the length of a day. For instance, seasonal and daily weather changes can influence the length of a day by several milliseconds every year, as can oceanic and atmospheric tides and variations in the atmosphere, oceans, groundwater and ice storage. Even the cyclic climate phenomenon called El Niño — associated with a weakening of the tropical Pacific trade winds and a strengthening of the mid-latitude westerlies — can slow down Earth's rotation, adding a millisecond onto a day, the researchers said.

Scientists record how long Earth takes to fully rotate each day by using a method called very long baseline interferometry (VLBI). Researchers developed VLBI in the 1960s to look at quasars, incredibly bright galactic centers created by matter falling onto a supermassive black hole. But researchers soon realized that because quasars barely move, the bright objects could act as reference points. Now, VLBI, which relies on radio dish signals around the world, helps scientists determine how Earth is moving relative to the quasars, according to NASA.

So, today, there is going to an extra second – and what are we going to do to that or how are we going to utilise that ??   In the past, leap seconds have caused problems for computer systems, often because scientists don't know about the extra second until the last minute (figuratively speaking). For instance, the extra second can create glitches galore for stock traders, computer programmers and airline companies unless their systems are prepared for the change.   The leap second added in 2012 caused problems for Reddit, LinkedIn, Gizmodo and FourSquare, Live Science reported in January."In the short term, leap seconds are not as predictable as everyone would like," Scientists added about one leap second every year from 1972 to 1999, but leap seconds have become less frequent since then; this June's extra second is only the fourth since 2000.

It's unclear why fewer leap seconds are needed nowadays, but sudden geological events, including earthquakes and volcanic eruptions, can affect Earth's rotation, at least in the short term, NASA scientists said. However, the leap second may be short-lived. There are several proposals to shelve the practice, but the decision won't be made until late 2015 at the earliest, according to NASA.

With regards – S. Sampathkumar

30^th June 2015.