5. 4. 3. 2. 1. 1... An extra second to see out 2016

Earth
Clouds over Australia are shown. Credit: NASA

As if 2016 has not been long enough, the year's dying minute will last an extra second to make up for time lost to Earth's slowing rotation, timekeepers say.

Countries that use Coordinated Universal Time—several West African nations, Britain, Ireland and Iceland—will add the leap second during the midnight countdown to 2017—making the year's final minute 61 seconds long.

For others, the timing will be determined by the they live in, relative to UTC.

"This extra second, or leap second, makes it possible to align astronomical time, which is irregular and determined by Earth's rotation, with UTC which is extremely stable and has been determined by atomic clocks since 1967," the Paris Observatory said in a statement.

The observatory houses the International Earth Rotation and Reference Systems Service (IERS), responsible for synchronising time.

"The sequence of dates of the UTC second markers will be: 2016 December 31 23h 59m 59s, 2016 December 31 23h 59m 60s, 2017 January 1, 0h 0m 0s," the IERS website states.

The adjustment is necessary because Earth's rotation is not regular—it sometimes speeds up, sometimes slows down, but is gradually slowing overall.

This is caused by factors including the Moon's gravitational Earth-braking forces, which give rise to the ocean tides.

The result is that astronomical time—based on the length of an Earth day— gradually falls out of sync with atomic time—which is measured by nearly 400 super-accurate dotted around the world.

Leap year, too

Atomic time or TAI, in turn, is used to determine UTC, used for civil timekeeping globally.

TAI is exactly 36 seconds ahead of UTC, a difference that keeps growing as leap seconds are added, and will reach 37 seconds on January 1.

When leap seconds were introduced in 1972, 10 seconds had to be added to UTC, followed by another roughly every 18 months thereafter, according to the National Institute of Standards and Technology (NIST) of the US Department of Commerce.

The last was added on June 30, 2015.

"Leap seconds are added in order to keep the difference between UTC and astronomical time (UT1) to less than 0.9 seconds," the NIST website explains.

"Usually leap seconds are added when UTC is ahead of UT1 by 0.4 seconds or more."

The process, it added, can create problems for data logging applications and telecommunications systems.

"Special attention must be given to these systems each there is a leap second."

2016 has also had a leap day—February 29—a four-yearly occurrence to keep the calendar synchronised with Earth's movement around the Sun.


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2016 will be one second longer

© 2016 AFP

Citation: 5. 4. 3. 2. 1. 1... An extra second to see out 2016 (2016, December 28) retrieved 20 October 2019 from https://phys.org/news/2016-12-extra_1.html
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User comments

Dec 28, 2016
As if 2016 wasnt long enough

Dec 29, 2016
Even the darkest cloud has its silver lining. I know it's just a sliver, but this is one more second Mr Anus Mouth has to wait for his inauguration.

Dec 29, 2016
This comment has been removed by a moderator.

Dec 29, 2016
Even the darkest cloud has its silver lining. I know it's just a sliver, but this is one more second Mr Anus Mouth has to wait for his inauguration.


Even antigoracle and his own monkeypuppetsock Bart_A has 3 braincells, and here he is, lining up for his bananas today:
http://phys.org/n...ups.html

Dec 29, 2016
Is there any reason why we can't let UT1 wander around as it is instead of arbitrarily correcting the time in leap seconds?

Dec 30, 2016
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Dec 30, 2016
I actually had to evaluate my company's software to see if there was a possible problem.

There wasn't, but we're glad we checked.

That's pretty much how it went with Y2K, too, for a lot of software companies.

Next up: the UNIX timestamp rollover in 2038. Considering how many 5ESS switches run UNIX, this one could be a real problem.

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