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'Leap Second' to Be Added on New Year's Eve This Year

'Leap Second' to Be Added on New Year's Eve This Year

Full story: <http://www.space.com/33361-leap-second-2016-atomic-clocks.html>

  Revelers will get to celebrate New Year's Eve for a tiny bit longer 
than usual this year.

A "leap second" will be added to the world's official clocks on Dec. 31 
at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time (UTC), 
which corresponds to 6:59:59 p.m. EST; the clocks will read 23:59:60 
before ticking over to midnight. The goal is to keep two different 
timescales in sync with each other.

The units of time had long been defined based on Earth's rotation 
relative to distant celestial bodies. But that changed with the 
invention of atomic clocks in the mid-20th century; scientists then 
decided to base the second on the natural vibrations of the cesium atom. 
[How to Build the Most Accurate Atomic Clocks (Video)]

These two timescales don't match up exactly, however. Measurements show 
that, because the moon's gravitational pull and other factors are 
gradually slowing Earth's spin, the rotation-based scale loses between 
1.5 and 2 milliseconds per day compared to atomic time — meaning the two 
diverge by a full second every 500 to 750 days.

Leap seconds are a way to make up for this difference. Since 1972, the 
International Earth Rotation and Reference Systems Service (IERS) — the 
organization that keeps track of time for the world — has added 26 leap 
seconds to atomic clocks, with the last such insertion coming on June 
30, 2015.

  The aim is to keep the two timescales within 0.9 seconds of each other.

"We can easily change the time of an atomic clock, but it is not 
possible to alter the Earth's rotational speed to match the atomic 
clocks," officials with the U.S. Naval Observatory (USNO), which 
maintains the Department of Defense's master clock, noted — wryly, it 
would seem — in a statement today (July 6).

While Earth's rotation rate is slowing, the effect is quite subtle.

"Confusion sometimes arises over the misconception that the occasional 
insertion of leap seconds every few years indicates that the Earth 
should stop rotating within a few millennia," USNO officials wrote. 
"This is because some [people] mistake leap seconds to be a measure of 
the rate at which the Earth is slowing. The 1-second increments are, 
however, indications of the accumulated difference in time between the 
two systems."

When leap seconds are added, they are always inserted on June 30 or Dec. 
31 of a particular year. In 1972, IERS officials called for a leap 
second to be inserted on both dates.
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'Leap Second' Tonight Will Cause 61-Second Minute
June 30, 2015 07:30am ET
Full story: 
<http://www.space.com/29795-leap-second-tonight-atomic-clocks.html>

  July will arrive a little late this year – one second late, to be exact.

Time will stand still for one second this evening (June 30) as a "leap 
second" is added to Coordinated Universal Time (UTC), the time standard 
by which most clocks are regulated. The International Earth Rotation and 
Reference Systems Service (IERS), which keeps track of time for the 
world, has decided that the extra second is needed to deal with Earth's 
irregular but gradually slowing rotation.

The extra second will be inserted just before midnight UTC — just before 
midnight GMT, and just before 8 p.m. EDT. Instead of rolling straight 
through from 23:59:59 to 00:00:00, UTC will tick over to 23:59:60 for a 
second. [June 2015 Gets An Extra Second (Video)]
Why does it happen?

The need for a leap second arises because of differences between the 
time as recorded on our atomic clocks and the time as recorded by the 
rotation of the Earth in its revolution around the sun. But what is the 
reason for this slowdown?

Recently, I had a chance to sit down with astrophysicist Neil deGrasse 
Tyson, director of New York City's Hayden Planetarium. We chatted about 
a number of different astronomical subjects, and one of them was the 
impending leap second.

"The moon is slowing us down," Tyson noted. "It's tugging on us. If it 
ultimately succeeds at this, Earth's rotation will be as slow as the 
lunar month, and we will always show the same face to one another in 
what is called a 'double tidal lock.'"

"But," Tyson added, "if you do the math, it will take longer than the 
lifespan of the sun for the moon to succeed at this. So it's not 
something you should worry about at this point."

Along with the moon, other factors contributing to the slowing of 
Earth's rotation include the sloshing of the planet's molten core, the 
rolling of the oceans, the melting of polar ice and the effects of solar 
gravity.

      3 30 245 MORE

'Leap Second' Tonight Will Cause 61-Second Minute
A "leap second" will be added to the world's atomic clocks on June 30, 
2015, to accommodate Earth's gradually slowing rotation.
Credit: NASA

July will arrive a little late this year – one second late, to be exact.

Time will stand still for one second this evening (June 30) as a "leap 
second" is added to Coordinated Universal Time (UTC), the time standard 
by which most clocks are regulated. The International Earth Rotation and 
Reference Systems Service (IERS), which keeps track of time for the 
world, has decided that the extra second is needed to deal with Earth's 
irregular but gradually slowing rotation.

The extra second will be inserted just before midnight UTC — just before 
midnight GMT, and just before 8 p.m. EDT. Instead of rolling straight 
through from 23:59:59 to 00:00:00, UTC will tick over to 23:59:60 for a 
second. [June 2015 Gets An Extra Second (Video)]
Why does it happen?

The need for a leap second arises because of differences between the 
time as recorded on our atomic clocks and the time as recorded by the 
rotation of the Earth in its revolution around the sun. But what is the 
reason for this slowdown?

Recently, I had a chance to sit down with astrophysicist Neil deGrasse 
Tyson, director of New York City's Hayden Planetarium. We chatted about 
a number of different astronomical subjects, and one of them was the 
impending leap second.

"The moon is slowing us down," Tyson noted. "It's tugging on us. If it 
ultimately succeeds at this, Earth's rotation will be as slow as the 
lunar month, and we will always show the same face to one another in 
what is called a 'double tidal lock.'"

"But," Tyson added, "if you do the math, it will take longer than the 
lifespan of the sun for the moon to succeed at this. So it's not 
something you should worry about at this point."

Along with the moon, other factors contributing to the slowing of 
Earth's rotation include the sloshing of the planet's molten core, the 
rolling of the oceans, the melting of polar ice and the effects of solar 
gravity.
This video isn't encoded for your device

Irregular slowdown

Since January 1972, timekeeping has, by international agreement, been 
maintained in accordance with the atomic time scale. The Earth is 
currently losing about three-thousandths of a second per day, and, 
atomic clocks are just over six-tenths of a second fast on UTC right 
now. The addition of the leap second will keep the difference from 
exceeding nine-tenths of a second.

Excluding this evening's insertion, leap seconds have been added 25 
times since 1972, most recently in June 2012.

Leap seconds are inserted, when needed, either on June 30 or at the very 
end of the year, on Dec. 31. In 1972, there were two leap seconds (in 
addition to that year also being a leap year). From 1973 to 1979, adding 
a leap second on New Year's Eve was an annual occurrence. But from 1999 
to 2011 it was necessary to add an extra second only twice (in December 
of 2005 and December 2008).
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Mr
12/22/2016 1:35:48 PM
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