The Moon Just… Disappeared Over 900 Years Ago

Photo credit: Anadolu Agency - Getty Images
Photo credit: Anadolu Agency - Getty Images


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  • In 1108, an account in the Peterborough Chronicle described a startling sight: a lunar eclipse that had blocked out the moon instead of turning it a deep copper hue.

  • Scientists, astronomers, and historians have long puzzled over the account.

  • Now, thanks to data from ice cores and tree rings, scientists have identified the eruption of Japan's Mt. Asama as the moon-blotting culprit.


Since the dawn of time, humans have been recording the strange things they've seen in the sky. Just look at this account from an observer of a lunar eclipse in the Anglo-Saxon Peterborough Chronicle, circa the year 1110:

"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."

Scientists have long puzzled over the cause of that mysteriously dark moon. After probing tree rings and ice cores for clues, Sébastien Guillet of the University of Geneva and his colleagues believe they've discovered the cause of the strange lunar phenomenon.

Typically, the moon takes on a reddish hue during a lunar eclipse. The size and composition of molecules in Earth's atmosphere, through a process called Rayleigh scattering, dictate what wavelengths of light will be refracted. (It's the same phenomenon that gives our planet its bright blue sky and brilliantly colored sunsets and sunrises; in this instant, it also turns the moon blood red.) During a lunar eclipse, red wavelengths slip through Earth's atmosphere and are reflected on the lunar surface.

So what would cause the moon to disappear completely during a lunar eclipse? It turns out the answer is pretty simple: volcanoes.

As volcanoes erupt, they belch sulfur-rich aerosols out into the atmosphere. The influx of these aerosols can actually blot out sunlight and affect Earth's climate. For example, global temperatures briefly plummeted in the years following the Philippines' Mount Pinotubo's 1991 eruption. The tricky part is identifying which eruption is responsible for the global cool down.

For this study, the scientists analyzed three ice cores: two from Greenland, which recorded periods of time between 1108 and 1113, and one from Antarctica, which recorded a period of time in 1109. The cores showed spikes of sulfates. Using these cores and their accompanying sulfate spikes, the scientists were able to pinpoint a likely date for the eruption: 1108.

In an effort to corroborate the ice core data, the study team turned to tree ring data collected across North America, Europe, and Asia. As they grow, trees capture data about Earth's atmosphere and can capture the impact that, say, volcanic eruptions have on weather.

The scientists then doubled back through the archives and unearthed additional records that featured lunar eclipses. Several of them, including the Peterborough Chronicle, noted a particularly dark lunar eclipse in 1108. All of this evidence, paired with geologic and historical records, suggests the eruption of Japan's Mount Asama in 1108 is likely to blame for the strange phenomenon.

But the mystery isn't completely solved yet.

Due to atmospheric conditions, it isn't likely that ash from a volcano that erupted in the tropics would have left the high sulfate marks in the Antarctic ice cores.

“Atmospheric circulation makes it very difficult for eruptions located at high latitudes to cross the tropics," Guillet told Science. That means another volcano must have erupted around the same time.

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