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Why the Earth is spinning faster and faster

The Earth in 2020 spun faster than usual and is expected to be even faster in 2021
The Earth in 2020 spun faster than usual and is expected to be even faster in 2021

Without a doubt, the year 2020 was very special and unforgettable for planet Earth. Why, literally everything was affected, including the weather, although this was not a product of the pandemic, as it was in the rest of the things.

The Earth in 2020 spun faster than usual, as if she herself wanted to end that pandemic year faster. Mathematically speaking, our planet broke the previous record for the shortest astronomical day, set in 2005. The shortest day of that year, July 5, saw the Earth complete a rotation of 1.0516 milliseconds faster than 86,400 seconds, which is the time it takes to rotate with respect to the Sun, which is equivalent to 24 hours or one mean solar day. Instead, the shortest day in 2020 was July 19, when the planet completed a spin 1,4602 milliseconds faster than 86,400 seconds. Further, 2020 included the shortest 28 days since 1960, and 2021 is forecast to be the shortest in decades.

When high-precision atomic clocks were developed in the 1960s, they showed that the length of an average solar day can vary in milliseconds (1 millisecond equals 0.001 seconds). These differences are obtained by measuring the rotation of the Earth relative to distant astronomical objects and using a mathematical formula to calculate the mean solar day. Before 2020 began, the shortest day since 1973 was July 5, 2005, when the Earth’s rotation took 1.0516 milliseconds less than 86,400 seconds.

An average day in 2021 will be 0.05 milliseconds less than 86,400 seconds
An average day in 2021 will be 0.05 milliseconds less than 86,400 seconds

According to scientists from the International Earth Rotation and Reference Systems Service (IERS) in Paris, France, the Earth’s rotational speed constantly varies due to the complex movement of its molten core, oceans and atmosphere, in addition to other effects. . They monitor the speed of Earth’s rotation and hope that the trend of having shorter days will follow us in 2021 as well.

According to his calculations, an average day in 2021 will be 0.05 milliseconds less than 86,400 seconds. Throughout the year, the atomic clocks will have accumulated a lag of about 19 milliseconds. For comparison: in recent years, they were a few hundred milliseconds faster per year. The last time an average day was less than 86,400 seconds in a full year was in 1937. If the Earth’s rotation becomes too out of sync with the super-constant rate of atomic clocks, a positive or negative leap second can be used to re-align them.

Since the leap-second system was introduced in 1972, the Earth’s rotation in general has been a bit slow. So far, there have been 27 interchangeable seconds and they have all been positive. In other words, everyone has added an extra second to our clocks, allowing Earth to catch up.

Earth has gotten faster and no leap second has been required since 2016 (Shutterstock)
Earth has gotten faster and no leap second has been required since 2016 (Shutterstock)

“It is quite possible that a negative leap second will be needed if the Earth’s rotation rate increases further, but it is too early to say if this is likely to happen,” said the physicist. Peter Whibberley of the National Physical Laboratory in the UK. “International discussions are also taking place about the future of leap seconds, and it is also possible that the need for a negative leap second could drive the decision to permanently end leap seconds,” he added.

Recently, however, Earth has gotten faster and no leap second has been required since 2016. If the Earth’s rotation continues to accelerate, at some point we might require a negative leap second. If this happens, our clocks would skip a second to keep up with the Earth.

To measure the actual length of a day, IERS scientists determine the exact speed of Earth’s rotation by measuring the precise times a fixed star passes a certain location in the sky each day. This measurement is expressed as Universal Time (UT1), a type of solar time.

UT1 is then compared to International Atomic Time (TAI), a highly accurate time scale that combines the output of about 200 atomic clocks maintained in laboratories around the world. The actual length of a day is expressed by the deviation of UT1 from TAI over 24 hours. Currently, the IERS does not show new leap seconds scheduled to be added.

According to the Service Earth Orientation Center leap seconds have their pros and cons. They are useful for making sure astronomical observations are in sync with the clock time, but can be a hassle for some data logging applications and telecommunications infrastructure. Some scientists at the International Telecommunication Union have suggested letting the gap between astronomical and atomic time widen until a “leap hour” is needed, which would minimize disruption to telecommunications. (Astronomers would have to make their own adjustments in the meantime.)

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About the author

Kim Diaz

Kim recently joined the team, and she writes for the Headline column of the website. She has done major in English, and a having a diploma in Journalism.

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