During an eclipse<\/a>, as the moon slowly begins to veil the sun, crescent-shaped shadows appear on the ground, and the world drops into an eerie daytime twilight. On Monday<\/a>, this will happen across a large swath of North America.<\/p>\n How did ancient cultures<\/a> respond to the darkness shrouding the light? In the past few decades, a scientific field called archeoastronomy has emerged to investigate questions such as this. Although it\u2019s a challenge to know what earlier humans saw when they stood in the shadow of an eclipse\u2014especially the further back we go\u2014archeoastronomers have used clues ranging from bark books to petroglyphs to ancient Chinese oracle bones to piece together these bygone stories of the cosmos.<\/p>\n If you’re enjoying this article, consider supporting our award-winning journalism by subscribing<\/a>. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.<\/p>\n Humans have been calculating the recurrence of solar eclipses for thousands of years. Many ancient cultures predicted these events mathematically using what Anthony Aveni, a pioneer of archeoastronomy and professor emeritus at Colgate University, calls the \u201csix-five beat.\u201d Solar and lunar eclipses usually recur every six lunar months or, more rarely, every five lunar months. Over time, by observing and calculating these intervals, the ancient Maya, Chinese and Babylonians all homed in on two predictable patterns for when identical solar and lunar eclipses would recur: one pattern spans 41 months, the other 47. Here\u2019s how these patterns, denoted as \u201cA\u201d and \u201cB\u201d, come about:<\/p>\n A.<\/b> The 41-month pattern: 6 + 6 + 6 + 6 + 6 + 6 + 5 = 41 months<\/i>, or some 3.4 years, after a total or near-total eclipse, an almost identical eclipse occurs.<\/p>\n Or:<\/p>\n B.<\/b> The 47-month pattern: 6 + 6 + 6 + 6 + 6 + 6 + 6 + 5 = 47 months<\/i>, or some 3.9 years, after a total or near-total eclipse, an almost identical eclipse occurs.<\/p>\n Then, after more time, these cultures found even more patterns. The Babylonians, for instance, noticed that after A + A + B + B + B, or 223 months (18.5 years), another identical sequence of eclipses occurred, called the Saros cycle. All these patterns, governed by the laws of planetary motion, were made by simply observing the sky with the naked eye\u2014so it\u2019s possible, or even likely, that these Maya, Chinese and Babylonian cultures had been using the six-five beat to predict eclipses even in prehistoric times, before written records. \u201cI have no doubt that people could do this a few thousand years [prior] and then pass that information on orally,\u201d Aveni says.<\/p>\n The oldest surviving depiction of an eclipse might be one from Loughcrew Megalithic Cemetery<\/a>, also known as the Hills of the Witch, near Oldcastle, Ireland. This site\u2019s Neolithic passage tombs, marked by large cairns, were built in the fourth millennium B.C.E.\u2014making them nearly a millennium older than Stonehenge.<\/p>\n Examining one of the cairns in 1999, archaeoastronomer Paul Griffin discovered a stone carving of overlapping concentric circles that he thought may depict an eclipse. He found that a near-total eclipse occurred at Loughcrew on November 30, 3340 B.C.E., around the time the cairns were built; this makes it plausible that the carving, called a petroglyph, did indeed represent an eclipse. But such a thing can\u2019t be proven, and Aveni says the concentric circles could have any number of possible meanings.<\/p>\n A few millennia later, the oldest verifiable solar eclipse records were carved in Anyang, China. This city, then called Yin, was the capital of the ancient Shang dynasty (1600\u20131045 B.C.E.)\u2014the first Chinese period that left behind written records. This legacy was rediscovered relatively recently, in 1899, when an Anyang pharmacist gave antiquarian and philologist Wang Yirong a prescription for a traditional remedy made by grinding up \u201cdragon bones.\u201d Wang was about to grind the bones when noticed that they were adorned with ancient Chinese inscriptions. These weren\u2019t dragon bones but oracle bones<\/a>: oxen shoulder blades and tortoise shells once used to predict the future. Eventually the artifacts were traced to a site near Anyang where some 50,000 inscribed oracle bones dating from 1400 to 1200 B.C.E. have since been discovered.<\/p>\n \u201cDivination played an enormously important role at the time,\u201d says Xueshun Liu<\/a>, a Chinese language lecturer in the Department of Asian Studies at the University of British Columbia. These bone inscriptions are the oldest known Chinese-language documents\u2014and they include descriptions of eclipses. During the Shang dynasty, when an eclipse loomed, specially marked oracle bones were placed over a fire; heating caused small cracks that were believed to be messages from deceased ancestors. A diviner, or oracle, then interpreted the cracks and inscribed prophecies on the bones.<\/p>\n One of the many oracle bones that mentions an eclipse says: \u201cThe king, reading the crack, said: \u2018There will be harm.\u2019 Another simply read, \u201cThe sun has been eaten.\u201d<\/p>\n Any given place on Earth\u2019s surface will only experience one total solar eclipse, lasting only a few minutes, every 375 years on average. So it\u2019s even rarer for this to coincide with another solar event called a coronal mass ejection, or CME. These occur when giant bubbles of plasma and magnetic field burst from the sun\u2019s corona, or its outer atmosphere. These ejections could be visible to the naked eye during a total solar eclipse, with the moon shielding everything but the sun\u2019s corona.<\/p>\n \u201cCMEs are not that rare. We get several of them during the day, especially during solar maximum,\u201d or the peak of the sun\u2019s 11-year activity cycle, says C. Alex Young<\/a>, associate director for science in the Heliophysics Science Division at NASA\u2019s Goddard Space Flight Center. But he notes that the odds of one coinciding with \u201cfour or so minutes of an eclipse are slim.\u201d<\/p>\n It\u2019s possible, however, that the ancient Pueblo people of Chaco Canyon, a city that thrived from C.E. 850\u20131250, may have witnessed such a spectacle. Evidence comes from Piedra del Sol, or \u201cRock of the Sun,\u201d a large boulder in modern-day New Mexico inscribed with numerous previously identified Chaco astronomical markers. In 1992 solar astronomer Kim Malville<\/a> was helping lead a three-week field trip for college students when he \u201cnoticed a peculiar petroglyph\u201d on the boulder. It looked like the sun was belching out rays. What\u2019s more, \u201cthere was a pecked mark where [Venus] would have been,\u201d says Malville, a professor emeritus of astrophysical and planetary sciences at the University of Colorado. Venus can be visible during an eclipse.<\/p>\nThe \u201cSix-Five Beat\u201d<\/h2>\n
On supporting science journalism<\/h2>\n
Cairn Carvings<\/h2>\n
Dragon Bones and Oracle Bones<\/h2>\n
A Dark, Belching Sun<\/h2>\n
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