The researchers compiled hundreds of records of lunar eclipses from across Europe, the Middle East, and Asia, documenting 187 eclipses between 1100 and 1300.
In particular, they searched for descriptions that provided information on the brightness and colour of the Moon during the eclipse. Most of these turned out to be from European monks or clerics, writing in Latin.
Based on these descriptions, the researchers ranked the colour and brightness of the Moon reported in each total eclipse. The brighter the eclipse, the clearer the atmosphere at the time: darker eclipses indicated a higher level of aerosol particles in the upper atmosphere – a marker of recent volcanic activity. TheConversation.com
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