The Strange Case of the Missing Moon in AD 1110

In the year AD 1110, the night sky turned dark as the Moon completely disappeared from view. Not for a few days as is usual, but the disappearance lasted months, perhaps even for more than a year. Now, scientists may have the reasons as to what caused this strange phenomenon.

Somehow, somewhere, a huge upheaval occurred in Earth's atmosphere around a millennium ago: the skies turned dark after a massive cloud of sulfur-rich particles moved through the stratosphere, eventually reaching Earth and now trapped deep within ice sheets or glaciers of Greenland.

The ice has preserved this evidence and this results in incredibly long timescales, which helps scientists pinpoint exact dates of events that are visible in the layers of an ice core. It has now been confirmed that the Moon's disappearing act did actually occur, but different theories have been put forward over the years as to the exact cause.

Scientists had long assumed that the sulphurous deposit was left by a major eruption unleashed in AD 1104 by Iceland's Hekla. Since the thin strip of ice ranks among the largest sulfate deposition signals of the last millennium, it sounded quite plausible.

However, more recent research concluded that a timescale named the Greenland Ice Core Chronology 2005 (GICC05) was showing the incorrect dates for some of the events and was off for about seven years[1].

The GICC05 information is what lead the new research team led by Sébastien Guillet from the University of Geneva to deduce that it could not have been the Hekla volcano's eruption that led to that specific phenomenon[2]. The team then looked into medieval records that described dark lunar eclipses that could correspond to this event.

"The spectacular atmospheric optical phenomena associated with high-altitude volcanic aerosols have caught the attention of chroniclers since ancient times," the team writes in their paper. "In particular, the reported brightness of lunar eclipses can be employed both to detect volcanic aerosols in the stratosphere and to quantify stratospheric optical depths following large eruptions."

The researchers discovered that in AD 1108 another massive volcanic eruption occurred, when Japan's Mount Asama erupted. Combining credible witness accounts and observation of tree ring formations, and other historical documentation, the team suggests that this eruption could have lead to the strange occurrence.

These observations aren't proof enough to concretely say they lead to the occurrences, however, putting all the different information together has lead the scientists to believe these forgotten massive eruptions created huge consequences on humanity.

[1] Sigl et al: Timing and climate forcing of volcanic eruptions for the past 2,500 years in Nature – 2015. See here.
[2] Guillet et al: Climatic and societal impacts of a “forgotten” cluster of volcanic eruptions in 1108-1110 CE in Scientific Reports – 2020. See here.