About 900 years ago, a skywatcher in England witnessed a total lunar eclipse that must have been baffling, even terrifying. Despite the fact that the night was clear and the stars shone bright, the Moon just...vanished.
During the unusually dark ecliptic blackout, the Moon was “so completely extinguished withal, that neither light, nor orb, nor anything at all of it was seen,” the person reported in a manuscript called the Peterborough Chronicle, adding that the dark Moon “continued nearly until day, and then appeared shining full and bright.” In the millennium since, nobody has come up with a comprehensive explanation for this bizarre occurrence.
To explain what might have caused this eerily black eclipse, which occurred on the night of May 5, 1110, a team of scientists examined tree rings, surveyed ice cores, and scoured historical archives. In a recent paper published in Scientific Reports, the researchers suggest that a “‘forgotten’ cluster of volcanic eruptions” from 1108 to 1110, possibly from Japan’s deadly Mount Asama, ejected a “dust veil” over Europe, which created the shadowy eclipse.
“I feel very lucky to have the opportunity to work with old trees, ancient texts, and ice-core data,” said lead author Sébastien Guillet, a paleoclimatologist at the University of Geneva, in an email. “I feel like a time traveler.”
That said, it takes a lot of time and concentration to accumulate natural records of ice cores and tree rings, let alone hunting for relevant information in historical sources from 12th century Europe, most of which are in Latin. “Sometimes you can spend days reading old texts without finding any relevant information related to weather or climate,” Guillet noted. “You have to be patient.”
Fortunately, the team’s efforts, which began in 2016, have culminated in a fascinating interdisciplinary collection of records.
As the authors note in the study, the “darkest total lunar eclipses” recorded since 1600 CE “have all been linked to large volcanic eruptions and the Peterborough Chronicle offers “one of the longest and most detailed accounts we are aware of for any dark lunar eclipse occurring between 500 and 1800 CE”, which sparked a search for likely volcanic events that may have led to it.
“The idea that the dark total lunar of May 1110 eclipse was connected to volcanism came actually quite easily,” Guillet said. “The darkness of the 1110 total lunar eclipse has, indeed, long caught the attention of astronomers and we knew about the existence of this intriguing eclipse long before we started to work on the 1108-1110 eruptions.”
Guillet and his colleagues looked for hints of major volcanic activity in ancient ice cores extracted from Greenland and Antarctica. These cores are treasure troves of information about the past climate, including volcanic eruptions, which can sprinkle ash and aerosols all around the world.
The team studied spikes in sulfate aerosols in the cores before and during the year 1110, when the dark eclipse happened, indicating that volcanic eruptions had belched fumes into the stratosphere around that time. When compared against the other known volcanic eruptions that occurred over the past 1,000 years, this volcanic event ranks seventh in terms of how much sulfur it injected into the atmosphere.
To bolster these observations, the researchers hunted down tree ring records that span this period, because these patterns inside trees grow in response to seasonal climate patterns. The rings suggested that the year 1109 in Western Europe was unusually cold and rainy, an anomaly that may have been caused or exacerbated by the global effects of a volcano spewing dust and ash into the skies.
The dreary weather documented in the tree rings is backed up by historical accounts that Guillet’s team collected. In Ireland, people fasted and gave alms to God so that the “heavy rain and bad weather in the summer and autumn might be dispelled,” according to the manuscript Annals of Inisfallen. As crops failed, famines in France broke out that “killed off many people and reduced countless numbers of rich people to poverty,” as recorded in the Chronicle of Morigny. Meanwhile, the Peterborough Chronicle, which contains the account of the dark lunar eclipse, attests that 1110 was “a very disastrous year.”
Though these climatic and social upheavals no doubt had complex origins, Guillet and his colleagues think the combination of natural and historical evidence points to a cluster of major eruptions as a factor. One likely culprit is Mount Asama, an active volcano on the main island of Japan. The volcano is known to have exploded in a catastrophic eruption in 1108, thanks to a contemporary statesman named Fujiwara no Munetada who chronicled it in a diary called Chūyūki.
However, it will take more research to track down the exact sources of this ancient stratospheric dust veil, as it’s probable that many eruptions contributed to this “disastrous year” of famines and creepy dark skies.
“We suggested in the study that Mount Asama in Japan contributed to sulfur deposition in Greenland but this hypothesis still needs to be confirmed,” Guillet said. “Hopefully one day we will be able to validate or invalidate this hypothesis.”
For instance, the team suggested that future research could focus on characterizing the “tephra,” or volcanic debris, found in ice cores from this time, as it could contain geochemical signatures that can be linked to specific volcanoes.
The new research is a reminder that our planet, and its civilizations, are deeply interconnected. A natural disaster in one corner of the world can throw communities thousands of miles away into turmoil, and can even darken the Moon on a clear night.
“Many more eruptions are evident from ice core records and several of them have never been studied in detail,” Guillet concluded. “Therefore, there's still plenty of work to do to better understand the influence of large eruptions on the climate system and to which degree these eruptions impacted (or not) past societies.”
Update : This article has been updated with comments from paleoclimatologist Sébastien Guillet.