Geometry of Solar Eclipses
Solar eclipses occur when the Moon passes between the Earth and the Sun, and casting a
shadow on the Earth. However, the type of eclipse which can be seen from a given location
depends on whether the Moon passes directly, or only partly, between the Earth and
Sun.This page attempts to explain how solar eclipses work, and the different types of solar
eclipse.
The diagrams here, by the way, are drawn to a wildly exaggerated scale.
Total Solar Eclipse
A total solar eclipse is when the Sun is completely covered by the Moon. This diagram
illustrates in more detail what happens during a total eclipse:
As it obvious the moon orbiting around the Earth passes between the Earth and Sun (i.e.
comes to a New Moon) at a point in its elliptical orbit when it is relatively close to the Earth.
In this way Moon blocks lights coming from earth and cast a dark shadow Umbra and a light
shadow Penumbra. The umbral part of the shadow (the umbra) is the area where the Sun is
totally obscured by the Moon. During a total eclipse, the shadow of the Moon falls upon the
Earth; in technical terms, we say that its magnitude is greater than or equal to 1.000. People
standing on those parts of the Earth, within the Umbra, see the Sun's face totally covered by
the Moon-hence called a total eclipse of the Sun
(Magnitude: It is the fraction of the sun's diameter covered by the moon at mid eclipse)
Partial Eclipses
A partial solar eclipse occurs when the Moon covers only part of the Sun, taking a "bite" out
of it. Looking again at the diagram above, you see that there is an area, outside the umbra,
where the Sun is only partly covered by the Moon; this is known as the penumbra, and it
covers a much larger area of the Earth than the umbra. Looking at the tip of the penumbra
pointer, for example, you will notice the Sun partially hidden by the Moon, so you see some
part of Sin is eclipsed and it not totally. The area of the Earth which falls within the
penumbra sees a partial eclipse of the Sun. Looking at it another way, we say that a
partial eclipse is an eclipse with a magnitude less than 1.000.
Partial Solar Eclipse, in which some part of the Sun is hidden
WARNING
It is important to bear in mind that when you are within a partial eclipse, the photosphere -the bright part of the Sun -- is still visible. You should never look at this directly, as it is
always capable of causing permanent eye damage, even when almost completely
covered.
The Annular Eclipse
An annular eclipse appears when the Moon covers most of central part of the Sun, but not
its edges, leaving a ring (or annulus) of the Sun visible around its edges. The next images
illustrates how an annular eclipse came into being:
Here, you can see the Moon in its elliptical orbit is farther from the Earth, and
the umbra is jnable to touch the Earth. However, the Moon is directly in front
of the Sun, so the parts of the Earth underneath it see a partial eclipse,
leaving a ring -- an annulus -- of the Sun. Technically; such an eclipse is
called a central eclipse with a magnitude less than 1.000.
The Hybrid Eclipse
A hybrid, (annular & total), eclipse is an eclipse which is appeared as annular by some
areas of the Earth, and total by others (and also as a partial eclipse over a much larger
part). This following images simplifies the occurrence of a hybrid eclipse.
In the above image, the Moon is just far enough from the Earth that the umbra can't touch
the Earth, so as the eclipse begins, the observers of this part of the Earth see an annular
eclipse.
As the Moon moves on, the umbra comes close to reach the Earth, the observers in the
centre of the eclipse track see a total eclipse. Such an eclipse would have a magnitude
greater than 1.000, but; during the ends of the eclipse, the magnitude is less than 1.000.
(being a partial or annular eclipse)
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