Gary sent in this link, www.sciencealert.com/mysterious-forgotten-volcanic-eruptions-in-history-… … we know that dendrochronologists were happy wen the ice core people were persuaded to to accept a 7 year discrepancy between the two disciplines a few years ago. This revolved around the date of the eruption of Mount Vesuvius and the odd thing that two narrow growth tree ring events only had one volcano between them – but there was one 7 years later. In making the switch all was deemed well but it seems some other historical volcanoes then became out of kilter. Evidence of sulphur in ice cores around 1110 was one such. Hekla, on Iceland, erupted around AD1104, on the new system, which meant another volcano was responsible. The investigation combed historical documents for a clue as atmospheric optimal phenomena associated with high altitude volcanic aerosols have intrigued mankind for some kind, especially when it caused a drastic fall in temperature. They searched chronicles for a clue and came across the Peterborough Chronicle of 1110, compiled by monks. It seems the brightness of lunar eclipses can be employed to detect the presence of aerosols in the stratosphere. According to NASA data seven total eclipses would have been visibile in Europe between AD1100 and 1120. An observer in the chronicle reported that the moon was at first bright but over the course of the night it got darker and darker