Smaller Day Observed in the Summer with the Development of Atomic Clocks

Thanks to the development of high-precision atomic clocks, almost imperceptible differences are now known. Shorter than the blink of an eye, this difference in the Earth's rotation is useful for astronomical studies, earthquakes, or solar storms.

Smaller Day Observed in the Summer with the Development of Atomic Clocks
Observations of the Changing Rotation of the Earth on June 29 with Atomic Clocks. Photo by Elena Mozhvilo / Unsplash

The Earth takes 24 hours to rotate on its axis, constituting what we know as a day. But that amount is not exact if measured with the high precision of atomic clocks, the technologies of current science in charge of measuring daily time, which identify very small variations, such as the one that occurred last June 29, when the rotation lasted 1.59 milliseconds less (a millisecond is the thousandth fraction of a second) and that date became a minimally shorter day.

According to the head of the magnetic service of the Institute of Geophysics of the UNAM, Juan Esteban Hernandez Quintero, these alterations can be detected with these instruments year after year and show that they have a cycle and that this shorter day occurs in the summer, at the end of June, and more frequently in July.

Explaining the phenomenon with a graph from the site, the scientist noted that in 2019 the shortest duration occurred on July 16, with 0.95 milliseconds less in the 24-hour rotation; in 2020 it happened on July 19, with 1.47 milliseconds less; in 2021, on July 9, with 1.46 milliseconds less; and in 2022 it broke the record on June 29, with 1.59 milliseconds less. Also, in the current year, on July 26, another faster, though not record-breaking, was recorded, which lasted 1.5 milliseconds less.

"A day is 24 hours long and a few seconds longer. Normal clocks that measure the time the day lasts, starting in the 1960s, are super-accurate, called atomic clocks, and they detected that on that day the Earth took a few milliseconds less to rotate. "As it took less time to rotate, the rotation movement was faster on that particular day by 1.59 milliseconds, an imperceptible amount for our daily life," he said.

The scientist said that the time spoken of in that phenomenon is small; however, it can be known more frequently from the 1970s and 1980s of the last century. Since then, 70 days were detected that lasted less than expected. Few lasted exactly 24 hours and sometimes a little more.

"We already know in calendars that the leap year is an adjustment that occurs every four years and generates an extra day in the year corresponding to February 29. This lack of time, speaking on another scale of milliseconds, will mean that when we have sufficient time, a second leap year will have to be added. This second leap will probably have to be adjusted as more days with this characteristic accumulate, "he explained about a hypothesis that is being discussed among the scientific community.

Some disciplines, such as astronomy, which uses precise control in the launch of spacecraft into space, or geophysics, which measures earthquakes and solar storms, require a precise study of time.

For example, to report the beginning of a magnetic phenomenon, we need the highest precision in time; also, when a solar storm or an earthquake is approaching, we need to report very precisely the duration and the beginning of the tremor for research purposes," exemplified the expert.

These small variations in diverse natural phenomena have probably always existed, but now technologies are capable of measuring them even if they are imperceptible to our eyes.

In the future, in an accumulated form, for example, over 50 years, they will provide information on the Earth's behavior and will be able to relate diverse phenomena to each other since the planet lacks perfect movement, the university professor added.

"There are phenomena that are disconnected, such as the Earth's gravitational field, which is studied independently. But at present, there are a series of satellites around our planet that are measuring that gravitational field. In the Earth's core, there could be some rearrangement of mass that makes the planet change its properties in the gravitational field, and those small variations could be relevant, "he concluded.