What about? Why will 2029 possibly last 1 second shorter?


Seemingly simple questions are often the most difficult to answer. In the What’s up section? we try to find the answer to such questions every week. This time: why will 2029 possibly last 1 second shorter?

What is a leap second, last used in 2016?

Do you remember the New Year’s Eve from 2016 to 2017? The countdown on December 31 lasted 1 second longer than usual. After 23.59.59 comes 23.59.60, before January 1, 2017 arrives. This has to do with the principle of the so-called leap second. Just as an extra leap day (February 29) is needed every 4 years, every now and then an extra second is needed in our calendar.

The leap day compensates for the Earth’s orbit around the sun, which in reality takes slightly longer than the 365 days we calculate for this. The leap second is precisely about the rotation of the Earth around its own axis, which deviates slightly from the 24-hour cycle that we use. Due to these time corrections, the rotations of the earth and our time calculation remain the same. There have been 27 of these leap seconds since 1972. The above-mentioned correction on December 31, 2016 has been the last to date. And there will certainly not be an additional leap second between 2035 and 2135, as we explain in this article.

Also read: What about? Why does the year start in January?

What is a negative leap second?

In the same article we also discuss the possible need for a unique phenomenon: the negative leap second. In that case, the year does not last 1 second longer, but 1 second shorter. Such an intervention has never taken place before, but since the corona year 2020, this possibility has become a lot more realistic. The year 2020 lasted a few milliseconds shorter than usual, because the Earth rotated faster on its own axis.

When will there be a negative leap second for the first time?

Scientists have since taken into account a scenario in which the negative leap second is needed as early as 2025 or 2026. However, it now appears that things will not progress that quickly. For the time being, 2029 seems to be the next possibility. This postponement is due to melting ice caps and the global spread of meltwater, as a result of climate change. Because this meltwater flows to the areas around the equator, the Earth has started to rotate on its axis a little more slowly. We can therefore postpone the need for a negative leap second a few more years, provisionally to 2029. But then the question remains how fast (or slow) the Earth will rotate on its axis by then.

What are the risks of this?

If there is indeed a definitive negative leap second, this will be communicated at least six months in advance. This preparation time is necessary, because taking away 1 mere second can have major consequences. The question remains how computer systems and atomic clocks react to such a deviation from our usual time calculation. There was also a leap second in 2012, which resulted in a number of technical malfunctions worldwide. What happens then if a second is not added, but rather taken away? Something that has never happened before? Maybe we’ll get an answer to that question in 2029.

Also read: What about? Why does Easter fall on a different date every year?

(Source: Archive, ANP, De Volkskrant, RTL News, CNN, Nature, LinkedIn. Photo: Shutterstock)

The article is in Dutch

Tags: possibly shorter


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