why the split second can disappear

On 27 occasions since 1972, a second has been added to our clocks to realign our timekeeping with that of the Earth’s rotation.

Will the calendar second disappear? Pressing, or not, this extra second was part of the discussions The General Conference on Weights and Measures was held this week in Parisbecause its addition “creates disruptions that risk causing serious malfunctions of essential digital infrastructures.”

Before we go any further, we must first remember what a leap second is: it is an extra second that is added when the clocks are no longer in phase with astronomical time because the Earth’s rotation around the sun is irregular.

“This extra second, or ‘leap’ second as it is called, makes it possible to link the irregular ‘astronomical’ time associated with the rotation of the Earth to the remarkably stable legal time scale established since 1967 by atomic clocks.” explains the Paris Observatory.

Difference between Coordinated Universal Time and Astronomical Time

It is in France that this one-second increment is set, because “it is a component of the International Service for the Earth’s Rotation and Reference Systems, located at the Paris Observatory”, which measures “the changes in the Earth’s orientation and who is therefore responsible for predicting and announcing these split seconds,” specifies the Paris Observatory.

“When the difference between Coordinated Universal Time and Astronomical Time exceeds 0.9 seconds, the difference is corrected by one leap second”. summarizes the Swiss Federal Institute of Meteorology.

Since 1972, 27 times a second have been added to our clocks, the night of June 30 to July 1, or December 31 to January 1. The last addition of a secular second took place on the night of December 31, 2016 to January 1, 2017.

“On January 1, 2017, at 1 a.m. (French time), the clocks will have to be set back by one tiny second.” then wrote the Paris Observatory. “Very exceptionally, minutes between 0h 59 minutes and 1 hour will last one second longer than normal, so 61 seconds instead of 60.”

However, leap seconds in the future can no longer be added, but removed. “Recent observations of the Earth’s rotation rate indicate that it may be necessary to introduce a negative leap second for the first time, which has never been considered or tested.” is it explained in the resolutions of the General Conference on Weights and Measures this Friday.

Why bother these seconds?

“Today it is discussed” about the maintenance of this fragile second. already explained in 2012 Paris Observatory. “They can in principle create synchronization problems in certain systems. It has therefore been a long-term issue to remove them,” the Swiss Federal Institute of Metrology wrote that same year.

The introduction of split seconds indeed creates “disruptions which risk causing serious malfunctions of essential digital infrastructures, such as global navigation satellite systems (GNSS), telecommunications systems and power transmission systems”, we can still read in recent resolutions of the General Conference on Weights and Measures.

In 2012 and 2017, some digital issues were indeed reported after the latter was added. BuzzFeed reported in 2012 how sites like Reddit, Foursquare, Yelp or even LinkedIn had crashed after the introduction of this second.

If this second is removed in the future, “besides a gap of one hour after 500 years, the most spectacular consequence of its removal would be, for the first time in human history, the complete disconnection of time from the celestial. movements”, the Paris Observatory recalled in 2012.

Salome Vincent BFMTV reporter

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