Эрдэмтэд 2700 гаруй жилийн өмнөх нарны хиртэлтийн тэмдэглэлийг ашиглан Дэлхийн эргэлтийн хурдны өөрчлөлтийг судалж байна.
МЭӨ 709 оны долдугаар сарын 17-нд эртний Хятадын Лу улсад тохиосон бүтэн нарны хиртэлтийг “Spring and Autumn Annals” хэмээх он дарааллын бичигт тэмдэглэн үлдээжээ. Энэхүү баримт нь нарны хиртэлтийг тодорхой дүрсэлсэн, он цагийг нь тогтоох боломжтой хамгийн эртний бичмэл эх сурвалж юм. Нагояагийн их сургуулийн судлаач Хисаши Хаяакава болон түүний баг орчин үеийн одон орон судлалын тооцоолол түүхэн бичвэртэй зөрчилдөж байсныг илрүүлжээ. Өмнөх судалгаануудад эртний Лу улсын нийслэл Цюфу хотын байршлыг бодит байдлаас нь найман километрээр буруу тогтоосон нь тооцооллын алдаанд хүргэж байсан байна.
Судлаачид хотын байршлыг археологийн баримтад тулгуурлан залруулснаар тухайн үеийн хиртэлтийн замыг илүү нарийвчлалтай тодорхойлж чаджээ. Энэхүү олдвор нь сарны таталцал болон Дэлхийн дотоод үйл явцаас хамааран гаригийн эргэлтийн хурд цаг хугацааны явцад хэрхэн өөрчлөгдсөнийг ойлгоход чухал ач холбогдолтой юм. Дэлхийн эргэлтийн хурд нь удаан хугацааны туршид хувьсан өөрчлөгдөж ирсэн бөгөөд үүнийг эртний хиртэлтийн мэдээллүүд баталдаг.
Түүнчлэн “Hanshu” хэмээх өөр нэгэн эртний сурвалжид хиртэлтийн үеэр нарны дээд болон доод хэсэгт шар өнгийн гэрэл ажиглагдсан тухай өгүүлжээ. Судлаачид үүнийг нарны титэм буюу нарны гаднах агаар мандлын үзэгдэл байж магадгүй хэмээн таамаглаж байна. Модны цагирагт хадгалагдсан нүүрстөрөгчийн шинжилгээгээр тухайн үед нарны идэвхжил өндөр байсан нь тогтоогдсон тул титэм харагдах боломжтой байсныг үгүйсгэхгүй. Гэсэн хэдий ч энэ нь тодорхой бус хэвээр байгаа бөгөөд эртний тэмдэглэлүүд нь Дэлхийн эргэлт болон нарны үйл ажиллагааны түүхийг нөхөн сэргээхэд үнэ цэнтэй мэдээлэл болсоор байна.
Дэлгэрэнгүйг эх сурвалжаас харах
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A solar eclipse recorded in China more than 2,700 years ago is giving scientists a fresh look at how Earth used to rotate. And the breakthrough came from something surprisingly simple: an eight-kilometer mistake in the location of an ancient city.
On July 17, 709 BCE, people in the ancient Chinese state of Lu watched the Sun disappear behind the Moon. Someone wrote down what happened, leaving behind what is now considered the oldest known datable written record explicitly describing a total solar eclipse. That short account survived in the Spring and Autumn Annals, a Chinese chronicle traditionally linked to Confucius.
More than two millennia later, researchers have found a new use for it. According to a study published in The Astrophysical Journal Letters, the ancient observation can help scientists better understand changes in Earth’s rotation. It may even tell us something about what the Sun looked like at the time.
An Ancient Eclipse That Wasn’t Supposed To Happen
The original record doesn’t offer much detail, just a single line scratched into a chronicle more than two millennia ago. It simply states:
“In fall, in the seventh month, on the rénchén day, the first day of the month, the Sun was totally eclipsed.”
For a long time, that seemed straightforward enough. But when scientists tried to recreate the eclipse using modern astronomical calculations, the numbers didn’t quite add up. The problem was Qufu, the ancient capital of Lu and the city associated with Confucius. According to earlier calculations, it was outside the path of totality. People there should have seen a partial eclipse, not the complete disappearance of the Sun. So where was the mistake?
Hisashi Hayakawa of Nagoya University and his colleagues turned to archaeological records. They discovered that previous studies had placed ancient Qufu roughly eight kilometers away from its actual historical location.
That might not sound like much, but eclipses are incredibly sensitive to location. The Moon’s shadow covers a relatively narrow strip of Earth’s surface, and moving just a few kilometers can completely change what an observer sees. Once the team corrected the coordinates, the ancient account made much more sense.
Earth’s Rotation Has Changed, Eclipses Prove It
We usually think of a day as 24 hours, give or take nothing. But Earth hasn’t always rotated at the same speed. The Moon’s gravitational pull gradually slows our planet through tidal interactions. Movements deep inside Earth, along with changes in the distribution of water and ice, can also affect how quickly it spins.
The changes are barely noticeable in a lifetime, but over millions of years, they really add up. Around 200 million years ago, during the Jurassic period, a day lasted roughly 23 hours. That meant a year contained about 380 to 385 days instead of today’s 365 or 366.
Ancient eclipses help scientists investigate these changes over shorter periods. Researchers can calculate where the Moon’s shadow should have fallen thousands of years ago. But the answer depends partly on how Earth was rotating at the time.
As explained by The Astrophysical Journal Letters, knowing where an eclipse actually occurred gives astronomers another way to refine their calculations. By correcting Qufu’s location, the team found that the 709 BCE eclipse could fit with a revised estimate of Earth’s ancient rotation. And that wasn’t the only interesting detail hiding in the historical records.
What Else Did Ancient Observers See Around the Sun?
Another Chinese text, the Hanshu, says the Sun appeared yellow above and below during the eclipse. Researchers think this may be an early description of the solar corona, the Sun’s outer atmosphere, visible only when the Moon fully blocks the solar disk.
To test the idea, the team reconstructed the Sun’s orientation during the eclipse and compared it with radioactive carbon preserved in tree rings, a record of ancient solar activity. The eclipse occurred shortly after a peak in the Sun’s roughly 11-year cycle, when prominent coronal structures would have been plausible.
What the ancient observers actually saw remains uncertain, and the yellow glow may not have been the solar corona. But the evidence points in that direction. More than 2,700 years later, their brief account is helping scientists piece together how Earth rotated in the past and what the Sun might have looked like.
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