What is the ‘leap second’ and why it will be eliminated from 2035

What is the ‘leap second’ and why it will be eliminated from 2035

Both are seconds.

But the duration of this unit of time is not the same if we are guided by the measurements of an atomic clock (of amazing precision) or by the rotation of the Earth.

That’s because, while the measurement based on the vibrations of atoms is incredibly stable, the time it takes for our planet to rotate on itself, on the contrary, varies.

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Interim second has been used 27 times since 1972 – in 2016 for the last time

The movement of the tides, the fact that the Earth is not a solid object, that it registers movements in its crust and that it has a core in a liquid state are some of the factors that contribute to this variability.

To compensate for the difference, the International Bureau of Weights and Measures (BIPM, in its acronym in French), located in Paris, agreed to periodically add a leap second – or intercalary second – when the difference between astronomical and universal time (dictated by clocks atomics) approaches 0.9 seconds.

All this may seem insignificant to us humble mortals, but it is not: the second is the base unit for measuring time in the international measurement system.

Without addition, over the years the distance between the two measures of time would only increase.

terrestrial globe

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Astronomical and atomic time are different

To synchronize the two clocks, the leap second has been used 27 times since 1972 – the last time in 2016.

Recently, however, the body in charge of establishing standards in the systems of units used around the world decided to eliminate this measure from 2035 onwards.

The problem, according to BIPM experts, is that it’s very difficult to predict exactly when you’ll need to add the extra second.

Therefore, many systems that rely on accurate measurements have developed their own methods to incorporate the latter. Some do it at the last moment of the last day of the year; others, on the first day of the year, for example.

This ends up jeopardizing the universality of time and, consequently, can pose a danger to all digital systems that are interconnected.

The BIMP decision, called “resolution D”, calls for the suspension of the leap second of 2035 at least until 2135, when the topic would be discussed again, possibly with new proposals developed by scientists to reconcile astronomical time with atomic time.

This “historic decision” would allow “a continuous flow of seconds without the discontinuities currently caused by irregular leap seconds,” said Patrizia Tavella, director of the BIPM’s time department.

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