DARK LUNAR ECLIPSE (UPDATED): On
Sunday night, Sept. 27th, the supermoon passed through the shadow of
Earth, producing a total lunar eclipse visible from the Americas,
Europe, Africa and parts of Asia. "It was one of the darkest lunar
eclipses I have ever seen," reports Kevin R. Witman, who sends this
picture from Cochranville, Pennsylvania:
Other observers (see the gallery)
also remarked on the darker hue of this lunar eclipse, compared to
others in recent years. What caused the change? Atmospheric scientist
Richard Keen of the University of Colorado offers one reason:
"Supermoon eclipses should be a bit darker. Because of its closeness to
Earth, a supermoon passes deeper into the shadow of our planet."
Working independently, Steve
Albers of NOAA and Helio Vital of REA/Brazil have suggested another
reason: aerosols in the atmosphere.
"Earth's stratosphere is no
longer completely clean of volcanic ashes," says Vital. "In fact,
lingering aerosols from the explosion of Calbuco, five months ago, may
be to blame for that excessive darkening."
Calbuco is a volcano in
Chile. After it erupted in April 2015, colorful sunsets were observed
around the southern hemisphere for months. Recently, Albers has noted an
increase in purple and yellow sunsets around his home town, Boulder CO,
and elsewhere. These are telltale colors of volcanic exhaust.
"A thin veneer of aerosols
from Calbuco may have now spread to the northern hemisphere," Albers
says. "In addition, we could be seeing the effects of residual smoke
from forest fires at high altitudes, or the general increase in
sulfate pollution that has been documented on a global basis."
Richard Keen, who is a
leading expert on volcanic aerosols and lunar eclipses, says "the Sept.
27th eclipse was about 0.5 magnitudes darker than expected for a clear
stratosphere. A slight layer of aerosols in the upper troposphere/lower
stratosphere might explain this. Also, the Moon passed through the
southern part of Earth's shadow, so southern hemisphere aerosols (such
as those produced by Calbuco) would have greater effect."
Keen says that he is still "crunching the numbers," and we may have more information soon...
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