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 30th 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
30th
June 2015.
