What was the total lunar eclipse of 2008 February 21 like?
Unique Light Pattern. The exact observed illumination pattern displayed by
the Moon during totality is unique for each eclipse and cannot be accurately
predicted in detail. However, it can be better understood by recalling a
simplified description of the event as it would be seen from the Moon, a very
sensitive screen that can be used as remote detector of volcanic aerosols in
the stratosphere.
Distorted Sun. As the
shadow of Earth would approach, a hypothetical observer on the Moon, standing
in the penumbra, would see the partially occulted solar disk gradually
disappear behind the much larger disk of our planet. The Sun would then look
more and more distorted due to refraction of sunlight grazing Earth`s atmosphere and would eventually become a very
bright protuberance on top of a segment of arc as it gradually hid behind Earth`s disk.
Fuzzy Penumbra-Umbra Border. Our atmosphere would be acting like a powerful lens
severely scattering, filtering and deviating sunlight from the penumbra into
the shadow cone cast by our planet. When
that protuberance would merge with the segment of arc, the observer would be
standing on the fuzzy penumbra-umbra border. That edge is neutral in color and
corresponds to the maximum gradient of light or the line along which the level
of sunlight would be falling off most sharply. It is also the frontier that
astronomers try to pinpoint as they time mid-crater contacts.
Bluish Cap and Outer Umbra. A couple of minutes later, selective stratospheric
absorption of red light by ozone molecules would be causing the residual
sunlight to acquire the bluish color frequently noticed shortly after the onset
of totality. At that point, a small
fraction of sunlight illuminating the currently aerosol-free upper layers of Earth`s atmosphere would be forming a bright bluish cap as
seen from the Moon.
Segments of Arc and
Intermediate colors. During the several minutes that would follow, the Sun
would further hide behind Earth`s disk and its
refracted image would become a series of annular segments that would continue
to fade, becoming thinner with time and gradually acquiring tints of green,
yellow and orange. During that brief period of time, observers could notice
intermediate colors in changing combinations of patterns and hues.
Mostly Red and