With so many mobile phones, televisions, consoles, tablets… we have less and less time to look at the sky. But in the Middle Ages, any unexpected fact on the celestial plane had to be an event. Especially for those monks cloistered within the walls of their monasteries.
Between the year 1100 and 1300 up to 64 total lunar eclipses were recorded. Medieval chroniclers faithfully documented 51 of them in their texts. And in five of these cases, they also reported that the moon was exceptionally dark.
These types of eclipses occur when Earth comes between the Moon and the Sun. The moon usually remains visible as a reddish orb because it is still bathed in sunlight that is bent around Earth by its atmosphere. But after a large volcanic eruption, there can be so much dust in the stratosphere that the moon almost disappears.
Monks in the Middle Ages recorded and described all kinds of historical events, including the exploits of kings and popes, major battles, and natural disasters and famines. Just as remarkable were the celestial phenomena that could herald such calamities. Mindful of the Book of Revelation, a vision of the end times that speaks of a blood-red moon, the chroniclers were especially careful to take note of the coloration of the Earth’s satellite.
An international team, led by the University of Geneva, has combed through medieval texts and compared them with data from ice cores and tree rings to accurately date some of the largest volcanic eruptions the world has seen in its entire history. .
Their results, as they explain in an article published in the journal Nature, have uncovered new details about one of the most volcanically active periods of all time, a phenomenon that could have triggered the Little Ice Age, a long cooling interval that It caused the advance of European glaciers and left a good part of Europe’s rivers frozen.
It took experts almost five years to examine hundreds of annals and chronicles from all over Europe and also from the Middle East in search of references to total lunar eclipses and their brightness and coloration, details that allowed linking the moon with the volcanic penumbra.
“One day I was listening to Pink Floyd’s Dark Side of the Moon album when I realized that the darkest lunar eclipses occurred a year or so after the main volcanic eruptions. Since we know the exact days of the eclipses, it opened up the possibility of using the sightings to narrow down when the eruptions should have occurred,†explains Sébastien Guillet, lead author of the study.
The researchers found that scribes in Japan also took note of lunar eclipses. One of the best-known storytellers, Fujiwara no Teika, wrote of an unprecedented dark eclipse observed on December 2, 1229: “the old had never seen it like this, with the location of the Moon’s disk not visible, as if it had disappeared.” during the eclipse… It really was something to fear.”
Stratospheric dust from large volcanic eruptions was not only responsible for the ‘disappearance’ of the moon. It also cooled summer temperatures by limiting sunlight reaching Earth’s surface. This in turn could lead to the ruin of agricultural crops, causing famines.
“We know from previous work that strong tropical eruptions can induce global cooling on the order of about 1°C over a few years,” says Markus Stoffel, also from the University of Geneva. “They can also cause rainfall anomalies with droughts in one place and floods in another,†he adds.
Despite these effects, the people of that time could not have even imagined that bad harvests or unusual lunar eclipses had anything to do with volcanoes: the eruptions themselves were undocumented, except for one of them.
“We only knew about these eruptions because they left traces in the ice of Antarctica and Greenland,” says Professor Clive Oppenheimer, from the Department of Geography at the University of Cambridge. “By bringing together the information from ice cores and descriptions from medieval texts, we can now make better estimates of when and where some of the largest eruptions of this period occurred.”
What makes these findings even more significant is that the interval between the years 1100 and 1300 is known from ice core evidence to be one of the most volcanically active periods in history. Of the 15 eruptions recorded in this paper, one that occurred in the mid-13th century rivals the famous Tambora eruption of 1815 that caused ‘the year without a summer’ of 1816.
