Posts Tagged ‘leap second’

Once upon a time, a leap-second …..

December 31, 2016

Leap seconds were invented in 1972 (in which year we had 2 leap seconds, one in June and one in December). In 26 of the 44 years since 1972 we have had leap seconds. A year with a leap second happens more often than a year without. Today we add the 27th leap second since its introduction.

A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to keep its time of day close to the mean solar time, or UT1. Without such a correction, time reckoned by Earth’s rotation drifts away from atomic time because of irregularities in the Earth’s rate of rotation. Since this system of correction was implemented in 1972, 26 leap seconds have been inserted, the most recent on June 30, 2015 at 23:59:60 UTC, and the next leap second will be inserted on December 31, 2016, at 23:59:60 UTC.

Having a leap-second is the new normal.

Deviation of day length from SI based day – Wikipedia


 

“Let there be cesium” and there was a leap second

June 28, 2015

On 30th June 2015 at 23:59:60, a leap second will be added before 1st July 2015, 00:00:00 because the difference between Coordinated Universal Time (UTC) and Universal Time (UT1) would have reached 0.9 seconds. Universal Time also known as Astronomical Time is based on the Earth’s rotation around its own axis, which determines the length of a day. Since 1972, 25 leap seconds have been inserted to synchronise these two clocks and this leap second will be the 26th. The differences are so irregular that the need for a leap second cannot be predicted more than about 6 months in advance.

The leap second is for synchronising the two clocks and not – directly – for compensating for the slowing down of the earth and the lengthening of the day. That adds about 1 second every 58,800 years (1.7ms per century). Since modern humans arrived on the scene some 200,000+ years ago the length of the day has increased by about 4 seconds.

International Atomic Time (TAI) is the “standard” used to synchronise the other two clocks and is built up by combining the output of some 200 highly precise atomic clocks worldwide and where the second is defined by the resonant oscillation frequency of cesium 133.

Atomic clocks use the second as the base unit and hours, days and years are taken to be multiples.

“The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.”

The wise men of our age believe (they cannot know) that this resonant frequency of the cesium 133 atom will remain “stable” for millions of years and is far more stable than the period of rotation of the irregular orbit of the earth around the sun or the even more irregular (and slowing) rotation period of the earth on its own axis.

All we measure, or try to measure, are periods of time – provided of course that time exists. Cesium would not have come into existence until about 3 minutes after the Big Bang, but time, presumably, began with the Big Bang. Initially there was only hydrogen and then came Big Bang Nucleosynthesis (BBN), which after about 10 seconds (cesium 133 seconds, though cesium still didn’t exist) started producing helium. The heavy elements came about 3 minutes after the BB and after about 20 minutes BBN ceased. Light would have been created as soon as the fusion of hydrogen started with the BB itself.

Rephrasing Genesis

The Big Bang was the Beginning and then came Fusion. The expanse was without form and void, and dark energy was over the face of the deep. And the Spirit of Gravity hovered over the face of the aether. And Gravity said, “Let there be Coalescence” and the stars of the heavens came to be. “Let there coalesce a Sun” said Gravity, and so there was light. “Let coalescence proceed” and under Gravity came the earth bathed in the light of the Sun. And the light was good. 

And the rest is history.

 


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