Solar eclipses
are of three types: total, partial and annular. The
type seen depends on what part of the Moon's shadow
passes over the observation point and
the distance between the Earth and the Moon at the
time of the eclipse.
An eclipse of the Sun occurs
when the Earth passes through the Moon's shadow.
The Moon's shadow has two parts: a fainter outer
region (in light gray) called the
penumbra and a dark inner shadow (in dark gray) called
the umbra.
Total
solar eclipses are the result of the Sun and
the Moon being almost exactly the same angular size as
we see them from Earth During a total eclipse the Moon
covers the bright disk of the Sun, but little or none
of the surrounding space. This allows us to see
features of the Sun that would otherwise be invisible,
except from outer space. These include the corona,
which stretches out from the Sun in all
directions, and solar prominences - large arch-shaped
structures observable in the corona.
During a total solar
eclipse, the
Sun's extensive outer atmosphere
or corona is a breathtaking sight.
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Total eclipses can
be observed only within the region of totality, a
very narrow band - up to 169 miles wide - where
the Moon's shadow falls as the Earth rotates. For
this reason, total eclipses are rare events in any
given geographical area and it is no wonder that
many eclipse-tour companies have sprung up, making
it easy for any eclipse-chaser to experience the
greatest sight of his lifetime.
Much more
common are partial solar
eclipses, in which the Moon obscures only
part of the Sun. Observers located in the much
broader outer shadow of the Moon (the penumbra)
see such an eclipse. At the edge of the penumbra,
the Moon seems to "take a bite out of the Sun".
Further within the penumbra, the Sun's disk takes
the shape of a
crescent.
Unfortunately, a partial eclipse is not as
dramatic as a total eclipse; even with
three-quarters of the Sun covered by the Moon,
daylight still looks quite ordinary.
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An annular eclipse
occurs when
the Moon is not quite big enough
to block out all the Sun.
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A special case of a
solar eclipse is known as an
annular eclipse. This occurs when the Moon
is farther from the Earth than normal, and hence
its apparent size is not quite sufficient to cover
the Sun completely. Therefore, even though the
Sun- Moon alignment is perfect, the Moon will
appear slightly smaller in diameter than the Sun
and a thin ring of sunlight will remain visible
around the dark silhouette of the Moon. The name
annular eclipse comes from the Latin annulus,
meaning ring.
One
should never pass up the chance of seeing the
splendor of such a celestial event. However great
care must be taken when watching a solar eclipse. Never look at the Sun unless you wear
special solar eclipse eyeglasses, and even more
importantly, make sure you have the proper filters if
you plan to observe the Sun through a telescope. |
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