According to NASA records based on astronomical retrocalculation, seven total lunar eclipses would have been observable in Europe in the first 20 years of the last millennium, between 1100 and 1120 CE.
Among these, a witness to a lunar eclipse that occurred in May 1110 wrote of the exceptional darkness of the Moon during the phenomenon.
“On the fifth night in the month of May appeared the Moon shining bright in the evening, and afterwards by little and little its light diminished, so that, as soon as night came, it was so completely extinguished withal, that neither light, nor orb, nor anything at all of it was seen,” an observer wrote in the Peterborough Chronicle.
Many astronomers have since discussed this mysterious and unusually dark lunar eclipse. Centuries after it occurred, the English astronomer Georges Frederick Chambers wrote about it, saying: “It is evident that this [eclipse] was an instance of a ‘black’ eclipse when the Moon becomes quite invisible instead of shining with the familiar coppery hue”.
Despite the event being well-known in astronomy history, though, researchers have never suggested it might have been caused by the presence of volcanic aerosols in the stratosphere, even though that’s the most likely cause, the new study suggests.
“We note that no other evidence of volcanic dust veil, such as a dimming of the Sun, red twilight glows and/or reddish solar haloes, could be found during our investigations for the years 1108–1110 CE,” the researchers write.
If the timing is right, then what volcano was responsible for the sulphur cloud, given Hekla is now out of the frame?