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Feb.
13, 2008: On Wednesday evening, February 20th, the
full Moon over the Americas will turn a delightful shade of
red and possibly turquoise, too. It's a total lunar eclipse—the
last one until Dec. 2010.
The
Sun goes down. The Moon comes up. You go out and look at the
sky. Observing the eclipse is that easy. Maximum eclipse,
and maximum beauty, occurs at 10:26 pm EST (7:26 pm PST).
Above:
A preview of the Feb. 20th lunar eclipse created by graphic
artist Larry Koehn. Click on the links to view labels for
other time zones: GMT,
AST, EST,
CST, MST,
PST, Alaska,
Hawaii.
A
lunar eclipse happens when the Moon passes through the shadow
of Earth. You might expect the Moon to grow even more ashen
than usual, but in fact it transforms into an orb of vivid
red.
Why
red? That is the color of Earth's shadow.
Consider
the following: Most shadows we're familiar with are black or
gray; step outside on a sunny day and look at your own. Earth's
shadow is different because, unlike you, Earth has an atmosphere.
The delicate layer of dusty air surrounding our planet reddens
and redirects the light of the sun, filling the dark behind
Earth with a sunset-red glow. The exact tint--anything from
bright orange to blood red is possible--depends on the unpredictable
state of the atmosphere at the time of the eclipse. "Only
the shadow knows," says astronomer Jack Horkheimer of the
Miami Space Transit Planetarium.
Transiting
the shadow's core takes about an hour. The first hints of
red appear around 10 pm EST (7 pm PST), heralding a profusion
of coppery hues that roll across the Moon's surface enveloping
every crater, mountain and moon rock, only to fade away again
after 11 pm EST (8 pm PST). No special filter or telescope
is required to see this spectacular event. It is a bright
and leisurely display visible from cities and countryside
alike.
While
you're watching, be alert for another color: turquoise. Observers
of several recent lunar eclipses have reported a flash of
turquoise bracketing the red of totality.
 "The
blue and turquoise shades at the edge of Earth's shadow were
incredible," recalls amateur astronomer Eva Seidenfaden
of Trier, Germany, who took the picture at right during the
European lunar eclipse of March 3-4, 2007. Dozens of other
photographers have documented the same phenomenon.
Right:
A "turquoise eclipse" photographed by Eva Seidenfaden
of Trier, Germany, on March 4, 2007. [Larger
image] [more]
The
source of the turquoise is ozone. Eclipse researcher Dr. Richard
Keen of the University of Colorado explains: "During
a lunar eclipse, most of the light illuminating the moon passes
through the stratosphere where it is reddened by scattering.
However, light passing through the upper stratosphere penetrates
the ozone layer, which absorbs red light and actually makes
the passing light ray bluer." This can be seen, he says,
as a soft blue fringe around the red core of Earth's shadow.
To catch
the turquoise on Feb. 20th, he advises, "look during
the first and last minutes of totality." That would be
around 10:01 pm EST and 10:51 pm EST (7:01 and 7:51 pm PST).
Blood
red, bright orange, gentle turquoise: it's all good. Mark
your calendar in vivid color for the Feb. 20th lunar eclipse.
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Editor's
note: This story is written for an American audience,
but not only Americans can see the eclipse. People in Europe
and western Africa are also favored. International maps and
timetables may be found here.
Author: Dr.
Tony Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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