why the leap second could disappear

On 27 occasions since 1972, a second has been added to our clocks to adjust our measurement of time with the Earth’s rotation.

Does the calendar second disappear? The removal, or not, of this extra second was part of the deliberations of the General Conference on Weights and Measures, held this week in Paris, because the addition “creates discontinuities that risk causing serious malfunctions in essential digital infrastructures.”

Before we go any further, we must first remember what a leap second is: it is an extra second added when 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 connect the irregular ‘astronomical’ time associated with the Earth’s rotation, with the extremely stable legal time scale defined since 1967 by atomic clocks”, explains the Paris Observatory.

The difference between Coordinated Universal Time and Astronomical Time

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

“Whenever 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 Meteorological Institute.

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

“On January 1, 2017, at 01:00 (French time), the clocks will have to be delayed by a small second,” the Paris Observatory wrote at the time. “Very exceptionally, the minute between 0h 59 minutes and 1 hour will last one second longer than usual, i.e. 61 seconds instead of 60.”

In the future, however, the leap seconds could 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”, it is explained in the decisions of the General Conference on Weights and Measures this Friday.

Why bother these seconds?

The maintenance of this leap second is “today discussed”, already explained in the 2012 Paris Observatory. “They can in principle generate synchronization problems in certain systems. It has thus been a question for a long time to remove them”, wrote the Swiss Federal Institute of Metrology in the same year.

The introduction of leap seconds actually creates “discontinuities that risk causing serious malfunctions in essential digital infrastructures, such as global navigation satellite systems (GNSS), telecommunications systems and energy transmission systems”, we can still read in the latest resolutions of the General Conference on Weights and Measures.

In 2012 and 2017, several digital problems had actually been reported, after the addition of this second one. BuzzFeed thus reported in 2012 how sites such as Reddit, Foursquare, Yelp or LinkedIn had crashed after the introduction of this second.

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

Salome Vincendon BFMTV journalist

Leave a Comment