The Moon "disappeared" from the sky some 900 years ago, and we may now know why

[lpetrich]

In 1110, The Moon Vanished From The Sky. We Might Finally Know What Caused It
Moon's mysterious disappearance 900 years ago finally gets an explanation | Live Science
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Climatic and societal impacts of a “forgotten” cluster of volcanic eruptions in 1108-1110 CE | Scientific Reports

From Live Science:

There's no use sugar coating it: According to one scribe in medieval England, A.D. 1110 was a "disastrous year." Torrential rainfall damaged crops, famine stalked the land — and, as if that wasn't bad enough, on one fateful night in May, the moon simply vanished from the sky.

"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," the unnamed scribe wrote in the Anglo-Saxon manuscript known as the Peterborough Chronicle. "As soon as night came, it was so completely extinguished withal, that neither light, nor orb, nor anything at all of it was seen. And so it continued nearly until day, and then appeared shining full and bright."

From Science Alert:

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.

Lunar eclipses get their coppery color from sunlight going through our planet's lower atmosphere and getting filtered. This filtering is why the Sun looks red when it is low on the horizon. Volcanic dust and droplets can increase the filtering enough to keep most of the light from getting through, thus letting much less light reach an eclipsed Moon and making a "black" eclipse.

 

[lpetrich]

The researchers were motivated to look through medieval chronicles for unusual atmospheric or astronomical events from discovering a big spike in sulfate aerosols in ice cores from Greenland and Antarctica. From Science Alert:

"A prominent discovery arising from this revised ice-core dating is a major and hitherto unrecognised bipolar volcanic signal with sulfate deposition starting in late 1108 or early 1109 CE and persisting until early 1113 CE in the Greenland record," Guillet and his co-authors explain in their paper, noting that evidence for the same event can also be seen in a similarly revised Antarctic ice core chronology.

So there were some big volcanic eruptions around then - eruptions whose emissions caused that bad weather and those famines and that dark eclipse.

In addition to witness accounts, the researchers also looked at tree ring evidence, which suggests 1109 CE was an exceptionally cold year (about 1 degree Celsius cooler in the Northern Hemisphere), based on significantly thinner tree rings.

It is hard to pin down which volcano, but there is one that the researchers ruled out: Hekla in Iceland, which erupted in 1104 CE. But the revised chronology does not fit that eruption. There is, however, a volcano that does fit.

While it's impossible to know for sure, the team thinks the most probable explanation is Japan's Mount Asama, which produced a giant, months-long eruption in the year 1108 – significantly larger than a subsequent eruption in 1783 that killed over 1,400 people.

A diary entry recorded by a statesman describes the 1108 event: "There was a fire at the top of the volcano, a thick layer of ash in the governor's garden, everywhere the fields and the rice fields are rendered unfit for cultivation. We never saw that in the country. It is a very strange and rare thing."