Early last year, scientists noted Earth was starting to spin a little faster around its axis. But recently the Earth has reduced its rotation speed.
The slowing of Earth's rotation makes the calculation of one day on Earth increase. It is estimated that this slowdown makes the calculation of world time have to increase by one second in the coming year.
On average, the planet completes a full rotation around its central axis every 86,400 seconds or 24 hours. But the rotation of the Earth is called imperfect, because there are many variations over time depending on the movement of the core, oceans and atmosphere.
In practice, each lap can vary by fractions of a second, which over time can add up to full seconds. Today, scientists keep track of time with the help of atomic clocks, which set the standard for Universal Coordinated Time (UTC).
This ultra-accurate clock measures time by observing the movement of electrons in atoms cooled to absolute zero (−273.15C). If there is a difference between the time determined by atomic clocks and the rotation of the Earth, scientists can add or subtract "leap seconds" to explain the difference.
A leap second is the insertion of one second into the calendar. One second is inserted with the intention that the time standard that is broadcast to the general public is maintained so that it is always close to the average time value of the Sun.
"Since the leap second system was introduced in 1972, Earth's rotation has generally been rather slow and so far, there have been 27 leap seconds, and they are all positive. In other words, they have all added an extra second to our clock, allowing Earth to catch up." said astrophysicist Graham Jones, quoted from Live Science, Saturday (10/30/2021).
Data collected by the National Institute of Standards and Technology (NIST), one leap second was added to the clock on New Year's Eve 2016.
On average, scientists have added a second jump to the clock every 18 months or so. As Earth spins faster in 2020, scientists are pondering the possibility of adding a negative leap second to make a difference.
The shortest day of the year, recorded on July 19, 2020, when the planet completed a full day of 1,4602 milliseconds faster than the average of 86,400 seconds.
According to a report in Time and Date, our planet has slowed down this year after the average day length increased on July 1 and September 30 by 0.05 milliseconds, more than in 2020.
The Earth, as a result, is spinning more slowly than in the first half of 2021, although its speed is still above average. Based on the current spin rate, scientists may need to introduce a negative leap second in about 10 years.
However, these conditions can also change without notice if the Earth suddenly accelerates or slows down its rotation without warning. The strange phenomenon makes it difficult for scientists to try to model this behavior in the future.
"We've tried internal modeling for the next two years or so. But we're having a hard time predicting for more than six months or a year," said Nick Stamatakos of the US Naval Observatory.
Scientists aren't sure what causes this long-term change in Earth's rotation. Sometimes, it is triggered by a strong earthquake as it can cause the Earth's mass to be reset.
Scientists also believe the loss of ice in Greenland has contributed to Earth's slowdown as a result of melting water moving away from the planet's poles.
