Wednesday (July 9th) is predicted to be an unusually shorter day 1.3 ms less than average as the Earth spun faster on its axis. However, according to TimeanDate.com, July 22nd and August 5th are expected to lose 1.38ms and 1.52ms, respectively. But why is it getting shorter this summer one day? How does that affect us?
Why does the Earth rotate faster?
A day on Earth lasts approximately 86,400 seconds or 24 hours. This is the amount of time it takes for a planet to rotate its axis completely. However, the speed of this rotation depends on many factors, such as the location of the sun and moon, and the gravity field of the Earth.
On July 9th, July 22nd and August 5th, 2025, the moon will be the farthest from the equator, changing the effect of gravity attraction on the Earth’s rotation. Think of the earth as the top of the spinning. If you place your finger in the center and rotate it, it won’t rotate immediately, as if it was holding it from the top and bottom. The same thing happens on Earth. As the moon approaches the poles, the Earth begins to spin faster and shorter than usual.
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Live Science contacted the International Earth Rotation and Reference Systems Service (IERS), an organization responsible for maintaining global time and reference frame standards, to see exactly how many milliseconds they lost on July 9th.
Related: Earth will spin much faster in the coming months – the shorter the days, the faster
How does losing 1.5 ms affect life on Earth?
For most of us, milliseconds or two losses are completely unaware. However, computers, GPS, banking systems, large telescopes and electrical networks rely on highly accurate synchronization to operate. On these systems, they are counted every millisecond.
“We send data very quickly and we need to tag everything, so our computers know where the data goes,” said David Gozard, a senior researcher at the University of Western Australia, who is a senior researcher specializing in precision measurements and satellite laser communications, to the Guardian.
Such accurate measurements are synchronized with a global reference time called the adjusted universal time (UTC).
What takes 1.5ms you might have missed on July 9th:
“[UTC] Dirk Piester, Dirk Piester and Dirk Piester, the time spread group 4.42 of the Physikalisch-Technische Bundesanstalt (PTB), the German National Institute for Spills, communicated to Live Science.
PTB is one of around 80 laboratories worldwide that is responsible for determining legal time in Germany and contributes to the calculation of UTC.
Unlike atomic clocks, which can calculate time on a scale of one billionth of a nanosecond, Earth’s rotation can be irregular. As a result, UTC is roughly independent of the length of the day, as determined by the rotation of the earth, Piester said.
“This means that the most accurate time management equipment used to achieve UTC does not take into account the current day length in daily operations,” he said. “The length of a clock in seconds corresponds to the definition of base time units in the international unit system.”
The variation in Earth’s rotation is often cancelled from each other or too small for us to notice. But over time, there are milliseconds added here and there to milliseconds. When this occurs, the IERS global timekeeper will add “Leap Second”.
“If there is a certain deviation in the length of the day from UTC, a jump of 2 seconds is applied to UTC,” says Piester. “This is to ensure that the time given by UTC corresponds to the time given by the rotation of the Earth within a second.”
However, in 2022, scientists voted to abolish the second jump by 2035. This is due to the confusion they cause in systems that rely on precise timekeeping.
Are the days on Earth shorter?
Over the past billions of years, the planet’s rotation has actually slowed down, which has made our days longer. For example, researchers in 2023 discovered that between about 1 billion and 2 billion years ago, a day on Earth was only 19 hours. Scientists believe this is primarily due to the gentle drift of the moon from our planet.
However, since 2020, scientists have noticed that the Earth has begun to spin slightly faster.
“We have a few days now that are slightly shorter than the last 50 years,” Piester said.
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