Scientists have been able to measure Earth's changing rotation thanks to the records of solar eclipses.
Scientists have been given locations for five solar eclipses thanks to a review of historical documents. The results are consistent with previous findings and give us a better understanding of how our planet is changing over time.
It seems like the length of a day is reliable. There are 24 hours in a day. Day after day after day, our clock counts that out. We live our lives on that beat. It's not a real thing.
There are a variety of factors that influence the rate at which our planet moves.
Consider the long term trend in which our days are getting longer. According to the fossil record, the days were just 18 hours long and half an hour shorter than they are now. We seem to be gaining a lot of time.
Scientists have figured out that Earth's days have a time variation of plus or minus 0.2 seconds every six years or so.
A short day last year was caused by a wobble in the rotation of the Earth. For something different, that's all.
The actual length of Earth's days can be influenced by a number of variables.
The measurement known as T is the most accurate timekeeping device we have and it is the discrepancy between the accepted length of a day which we all set our watches to.
It's important when it comes to solar eclipses. The Moon's shadow will fall on a planet that is under UT, because the positions of the Sun and the Moon are calculated and predicted using the same method. You need to know the difference between the two times in order to make a prediction about where the eclipse will be visible.
It works in a different way. You can work out the exact time and location of the solar eclipse if you have the right information. Scientists have been able to work out T from historical records.
Three scientists, Hisashi Hayakawa of Nagoya University, Koji Murata of the University of Tsukuba, and Mitsuru Sma of the National Astronomical Observatory of Japan, studied historical documents from the Byzantine Empire to do the same thing.
There is a scarcity of solar eclipse records from the 4th to the 7th century. It's difficult. The records don't usually include details that are relevant to modern studies. The researchers were able to identify five solar eclipses from previously unanalyzed records.
"Although original accounts from this period have mostly been lost, quotations, translations, etc., recorded by later generations provide valuable information."
Confirmation of eclipse totality, daytime darkness to the extent that stars appeared in the sky, was one of the requirements. We were able to identify the probable times and locations of five total solar eclipses from the 4th to 7th centuries.
The values for T that the team was able to derive were in line with previous estimates.
There were some things that weren't expected. The site of observation for the totality of the eclipse was Constantinople.
The author describes the eclipse that took place on July 19th when Theodosius was a teenager.
Philostorgius lived in Constantinople until he died. He's most likely to have seen the solar eclipse from there. The previous model for T would have placed Constantinople outside the path of totality, so the team has been able to adjust T for this time.
The other records show small changes.
The new T data indicates that the Tmargin for the 5th century should be revised upward, whereas those for the 6th and 7th century should be revised downward.
The changes have a lot of implications. They place tighter constraints on the variability of Earth's rotation on century timescales and may inform future studies of other geophysical phenomena.
The research has been published in a journal.
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