Records from a millennium and a half ago have allowed scientists to refine measurements of Earth’s rotational changes.
How has Earth’s rotation changed since its formation, or in other words, how have these changes over time impacted our planet? These questions have always posed a challenge for scientists seeking answers.
Total solar eclipse captured in Australia in 2012. (Photo: Getty).
Recently, a group of scientists from Nagoya University, Tsukuba University, and the National Astronomical Observatory of Japan revealed that a careful examination of historical documents from the Byzantine Empire, dating back over a millennium, has provided them with new insights into the variable speed of Earth’s rotation.
These documents also fill a significant gap in the recorded history of Earth’s rotation spanning from approximately the 4th to the 7th century AD.
It is known that Byzantine documents are ancient handwritten records that note the times and locations of solar eclipses occurring throughout the year.
According to researcher Koji Murata from Tsukuba University, although the descendants from this period have been lost, the citations and translations recorded by later generations have provided valuable information.
Specifically, based on this documentation, scientists hypothesize that a day was only 18 hours long 1.4 billion years ago, and shorter by about half an hour (equivalent to 23.5 hours) around 70 million years ago.
They estimate that our planet is slowing down, with the length of each day increasing by approximately 1.8 milliseconds per century.
Earth is gradually slowing down. (Photo: Shutterstock).
However, they discovered unusual fluctuations occurring over a span of about six years, causing the length of a day to increase or decrease by 0.2 seconds. This anomaly seems to be the result of a wobble in Earth’s rotational axis.
“We found reliable data regarding the location and timing of solar eclipses, including five total solar eclipses that occurred from the 4th to the 7th century in the Eastern Mediterranean, in the years 346, 418, 484, 601, and 693 AD,” Murata stated.
From this information, scientists were able to calculate the ΔT (delta-T) value – known as a measure of the impact on Earth’s deviation from its natural rotational cycle.
Previously, it was understood that Earth’s rotational speed depended on various factors, including climate conditions, environmental influences, atmospheric drag, and the Moon’s expanding orbit. However, thanks to recent research, we now know that the frequency of solar eclipses can also have an effect.
It is noted that the ΔT value at the beginning of 1902 was approximately 0. However, by 2002, this value was around 64 seconds. Thus, Earth’s rotations during that period had extended by about 64 seconds.
