This article originally appeared on VICE US.
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,” possibly from Japan’s deadly Mount Asama, ejected a “dust veil” over Europe, which created the shadowy eclipse. Since the moon is usually illuminated by the sun, anything that blocks the sun's light – such as the earth passing between the moon and the sun during an eclipse, or in this case, ash – can block or scatter that light.
Led by Sébastien Guillet, a paleoclimatologist at the University of Geneva, the authors note in the study that the “darkest total lunar eclipses” recorded since 1600 CE “have all been linked to large volcanic eruptions.” Unlike the moon, stars emit their own light and so weren't affected by the phenomenon. However in an email, Guillet pointed out that "star dimming has also been observed after large volcanic eruptions" by astronomers in the early 1800s.
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,” the team said, which sparked a search for likely volcanic events that may have led to it. 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 noted that there were spikes in sulfate aerosols in the cores before and during the year 1110, when the dark eclipse happened, indicating that a volcano had belched its fumes into the stratosphere around that time.
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. 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 possible that many eruptions contributed to this “disastrous year” of famines and creepy dark skies. 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.