An ex­tra sec­ond to see out 2016

Kuwait Times - - FRONT PAGE -

PARIS: 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 time zone 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 syn­chro­niz­ing 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 su­per­ac­cu­rate atomic clocks dot­ted around the world. 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 time there is a leap sec­ond.” 2016 - an­nus hor­ri­bilis for many with its rash of celebrity deaths and po­lit­i­cal up­sets - has also had a leap day - Feb 29 - a four-yearly oc­cur­rence to keep the cal­en­dar syn­chro­nized with Earth’s move­ment around the Sun.

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