for National Geographic News
A "disappearing" moon that preceded an unusually bitter winter in China was most likely the result of a mysterious volcanic eruption in the 1700s, a retired NASA scientist says.
Astronomer Kevin D. Pang collected evidence from the fields of geology, biology, and Chinese history that suggests a major eruption belched out enough dust and gas to completely blot out the moon during a 1761 total lunar eclipse.
A total eclipse occurs when the moon enters completely into Earth's shadow. (Watch video of the February 2008 lunar eclipse—the last total eclipse of the moon until December 2010.)
Lunar eclipses can vary in brightness and color based on the angle of the moon's path and the composition of Earth's atmosphere.
While no sunlight hits the moon directly, some gets filtered by Earth's atmosphere and is bent toward the moon, causing it to shine in hues ranging from bright orange to blood red.
"But when there's a large volcanic eruption," Pang said, "the moon can drop in brightness by a million times, or in some cases disappear altogether."
Pang presented his results last week during the 213th meeting of the American Astronomical Society in Long Beach, California.
Heavy amounts of particles in the air could explain why, in May of 1761, astronomers reported that the moon appeared very dark or disappeared altogether, even with the aid of telescopes.
An atmosphere clogged by a powerful volcanic eruption would also lead to global cooling and trigger extended bouts of strange weather, experts say.
(Related: "Ancient Global Dimming Linked to Volcanic Eruption" [March 19, 2008].)
To test his theory, Pang searched the scientific literature about tree rings and ice cores from Antarctica and Greenland. He found evidence of a "volcanic winter" around the same time as the dark eclipse.
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