One of the first images of the Earth, clicked by LI4 Camera of Chandrayaan-2’s Vikram lander, as viewed from space Credit: ISRO/File image

Scientists have suggested that planet Earth is spinning faster than it has in the last half of the century. This means a day on Earth is now shorter than 24 hours.

According to scientists, an average day on Earth will be 0.05 milliseconds shorter than the usual 86,400 seconds that make up the 24 hours in a day. It would amount to an accumulated lag of about 19 milliseconds on the atomic clocks by year-end, they suggest.

The year 2020 had 28 shortest days and now 2021 is going to be an even shorter year in these terms.

Atomic clocks keep ultra-precise records of day length and they have been doing so since the 1960s. These clocks have suggested that Earth has been taking slightly less than 24 hours to complete its rotation for as long as 50 years. It is reported that the shortest day on Earth was recorded on July 19, 2020. The day was 1.4602 milliseconds shorter than 24 hours on that day.

Officially, the International Earth Rotation and Reference Systems Service (IERS) measures the length of a day. Scientists at the IERS find out the exact speed of the planet’s rotation by measuring the precise moments a fixed star passes a certain location in the sky each day.

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The measurement is a type of solar time, which is expressed as Universal Time (UT1). This solar time is compared with the International Atomic Time (TAI). The TAI is a precise time scale, which takes and combines the output from around 200 atomic clocks across the world. The deviation of UT1 from TAI over 24 hours reveals the actual length of the day.

If the rotation of the planet and the steady beat of atomic clocks go out of sync, scientists can use a positive or negative leap second to bring them back in sync.

A leap second is added to the Coordinated Universal Time (UTC) to keep it in sync with the astronomical time, according to the National Institute of Standards and Technology, US.

With the change in rotation speed, there has been an ongoing debate about the need to subtract a second from time to reflect the change. A ‘negative leap second’ has never been done before but 27 leap seconds have been added, when Earth was taking slightly longer than 24 hours to finish its rotation for over a decade.

While leap seconds are great to keep astronomical observations synced with clock time, they can prove to be a problem for telecommunications infrastructure as well as data-logging applications.

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