{"id":658935,"date":"2026-10-27T21:12:18","date_gmt":"2026-10-27T21:12:18","guid":{"rendered":"https:\/\/www.newsbeep.com\/il\/658935\/"},"modified":"2026-10-27T21:12:18","modified_gmt":"2026-10-27T21:12:18","slug":"a-2700-year-old-chinese-eclipse-record-is-helping-scientists-reconstruct-the-earths-rotation","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/il\/658935\/","title":{"rendered":"A 2,700-Year-Old Chinese Eclipse Record Is Helping Scientists Reconstruct the Earth’s Rotation"},"content":{"rendered":"

\"Composite<\/a>This image combines many exposures of different durations taken to reveal aspects of the widely-viewed total solar eclipse of 21 August 2017, which was visible from the United States. Image credits: EOS.<\/p>\n

On July 17, 709 BCE, the Sun vanished over an ancient Chinese capital. Someone recorded the extraordinary event, preserving a brief account that would survive for more than 2,700 years.<\/p>\n

Now, that ancient observation is helping scientists reconstruct how fast Earth rotated thousands of years ago. By combining historical texts, archaeology, and modern astronomical calculations, an international research team has resolved a long-standing discrepancy in the eclipse\u2019s location. Their work also offers a tantalizing glimpse of what the Sun itself looked like in antiquity.<\/p>\n

An eclipse that shouldn\u2019t have happened<\/p>\n

The record comes from the Chunqiu<\/a>, or Spring and Autumn Annals, an ancient Chinese chronicle traditionally associated with Confucius. It contains 37 reports of solar eclipses, three of which explicitly describe totality. <\/p>\n

The earliest is from 709 BCE, making it the oldest known datable written account that explicitly identifies a total solar eclipse<\/a>.<\/p>\n

The text is straightforward: \u201cIn fall, in the seventh month, on the r\u00e9nch\u00e9n<\/a> day, the first day of the month, the Sun was totally eclipsed.\u201d<\/p>\n

But there was a problem.<\/p>\n

\"Old<\/a>Ancient Chinese text from the Spring and Autumn Annals that contains humanity\u2019s earliest datable written record of a total solar eclipse from 709 BCE. The text states \u201cIn autumn, in the seventh month, on the renchen day, the first day of the month, the Sun was totally eclipsed.\u201d The term \u201crenchen\u201d refers to a specific day in the traditional Chinese 60-day calendar cycle. Image courtesy of the National Archives of Japan.<\/p>\n

When researchers reconstructed the eclipse using modern astronomical models, something didn\u2019t fit. The observation was made in the ancient capital of Qufu, the hometown of Confucius. But Qufu appears to lie outside the Moon\u2019s path of totality<\/a>. According to those calculations, the Sun would have remained partially visible.<\/p>\n

So, why did these people report seeing a total eclipse?<\/p>\n

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An eight-kilometre clue<\/p>\n

To get the answer, researchers focused on archaeology. Hisashi Hayakawa of Nagoya University and his colleagues revisited archaeological reports documenting the location of Qufu during the ancient state of Lu.<\/p>\n

They discovered that earlier astronomical studies had used coordinates roughly eight kilometres away from the historical city\u2019s actual location. As it turns out, that relatively small distance made all the difference.<\/p>\n

During a total solar eclipse, the Moon casts a relatively narrow shadow across Earth\u2019s surface. Moving an observation point by just a few kilometres can mean the difference between complete darkness and a partially obscured Sun.<\/p>\n

\"Illustration<\/a><\/p>\n

Using the corrected coordinates, the researchers reassessed the eclipse and found that the ancient account could fit with a revised estimate of Earth\u2019s rotation.<\/p>\n

And that revealed something far more interesting than a misplaced city.<\/p>\n

Earth\u2019s clock is not constant<\/p>\n

We tend to think of a day as an unchanging 24 hours. But Earth doesn\u2019t rotate at a perfectly constant rate.<\/p>\n

Over geological timescales, tidal interactions<\/a> with the Moon gradually slow our planet\u2019s spin. Other processes, including movements within Earth\u2019s interior and changes in the distribution of water and ice, also affect its rotation. These variations are tiny on a human timescale. Over thousands of years, however, they accumulate.<\/p>\n

During the Jurassic, around 200 million years ago, when dinosaurs roamed the Earth, a day lasted roughly 23 hours instead of today\u2019s 24. That meant approximately 380\u2013385 days in a year.<\/p>\n

Of course, over human scales, the differences are much smaller, and that\u2019s when events like eclipses become important. Astronomers can calculate where the Moon\u2019s shadow would have fallen thousands of years ago. But those calculations depend on how Earth was rotating at the time. So basically, if you know where an eclipse was, you can calculate how the Earth was rotating at the time. With this eclipse, researchers were able to finesse records about Earth\u2019s rotation at the time.<\/p>\n

But that\u2019s not the only interesting thing they found.<\/p>\n

A strange yellow glow around the Sun<\/p>\n

\"Image<\/a>Solar corona viewed by Proba-2. Image credits: NASA.<\/p>\n

A later Chinese historical work, the Hanshu, describes the eclipsed Sun as appearing yellow above and below.<\/p>\n

Scientists have long suspected that this passage might refer to the solar corona<\/a> \u2014 the Sun\u2019s outer atmosphere, normally hidden by its overwhelming brightness but visible during a total eclipse.<\/p>\n

The researchers reconstructed the Sun\u2019s orientation during the ancient event and compared the possible coronal structures with estimates of solar activity derived from radioactive carbon preserved in tree rings.<\/p>\n

The two sources were broadly consistent. The eclipse occurred shortly after a peak in the Sun\u2019s approximately 11-year activity cycle, when prominent coronal structures would have been plausible.<\/p>\n

It\u2019s hard to prove something like this, but it\u2019s definitely plausible.<\/p>\n

The study highlights an unusual partnership between history and astronomy.<\/p>\n

Ancient Chinese observers weren\u2019t trying to measure changes in Earth\u2019s rotation or reconstruct solar magnetic activity. They were recording an extraordinary event, often interpreted through the politics and beliefs of their time.<\/p>\n

Yet their records have become scientific evidence.<\/p>\n

Nearly three millennia later, an eclipse that lasted only minutes is still helping researchers investigate two constantly changing worlds: the Earth beneath our feet and the Sun above our heads.<\/p>\n

The study was published in The Astrophysical Journal Letters<\/a>.<\/p>\n


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