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Great Comet of 1811

November 1, 2011

This year marks the two hundredth anniversary of a heavenly spectacle: the Great Comet of 1811, which graced the skies for most of that year.

A comet is a “dirty snowball” — frozen water and gases mixed with rock. It spends most of its time in the frigid reaches of the outer solar system. When it gets close to the warm Sun, though, it grows a long, glowing tail.

The Great Comet of 1811 never came very close to either the Sun or Earth. It more than made up for that, though, with its enormous size. As a result, the comet grew brilliant and remained visible for many months.

Astronomers first spotted the comet on March 25th, long before its closest approach. It passed nearest the Sun in September, and nearest Earth on October 20th. Even so, it never came closer to either body than the 93 million miles that separate the Sun and Earth.

But because of its great size, at its peak the comet glistened as brightly as some of the brightest stars. Not until the following January did it fade below the reach of the unaided eye. No other comet in recorded history had remained visible to the unaided eye for so long — and none would until the 1990s, when Comet Hale-Bopp surpassed it. That was another large comet that never ventured close to either the Sun or Earth yet put on a great show.

To some, the Great Comet of 1811 portended earthquakes and war, while others thanked it for an especially good year for wine. More about that tomorrow.


Script by Ken Croswell, Copyright 2011


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