INTRODUTION:
An Eclipse may be defined as a celestial phenomenon
wherein there is a partial or total obscuring
of one celestial body by the other. Eclipses have
been around for a long time. In the early years,
when an eclipse occurred, man his in fear believed
that the fury of the gods was being unleashed
upon him. Anaxagoras was said to be first man
to proclaim that there was a rational explanation
for eclipses. His views were later echoed by other
scientists such as Aryabhatta and led to man’s
deduction of why eclipses occur. In ancient times,
the Stonehenge was considered to be a predictor
of eclipses, by virtue of the fact that many of
the large stones are lined up to mark equinoxes
and solstices. [Newham, 2000]
The Moon, being a satellite of the Earth, revolves
around it, while the Earth is simultaneously revolving
around the sun. Therefore, sometimes, the moon,
earth and sun move into a straight line, in which
instance light from the sun is blocked, and depending
upon the positions of the sun, the earth and the
moon, two types of eclipses occur. They are:
(a) Solar eclipse
(b) Lunar Eclipse
SOLAR ECLIPSE:
When the moon lies between the sun and the Earth,
thus projecting a shadow back to the Earth and
obscuring the view of the sun, a solar eclipse
is said to occur. The Moon-Earth orbit and the
Sun-Earth orbits intersect, at a point that is
referred to as a node and results in an eclipse.
Light travels in straight lines from every part
of the son to the earth, falling from various
angles on the Earth. However since the moon is
a smaller globe than that of the Earth, the resulting
shadow thrown back by the Moon on the Earth would
be shaped like a cone – broadest on the
surface of the Earth and shrinking to a point
– an triangular area which would be completely
black and is referred to as the “Umbra”
shadow. Therefore a person standing in this umbra
region perceives the sun as being completely black.
However in the peripheral areas, the rays of the
sun filter through partially and these partially
darkened areas are referred to as “Penumbra”.
Based upon this, three kinds of solar eclipses
are identified:
(a) Total eclipse : when standing in umbra shadow
(an area that is at most, a hundred miles wide)
(b) Partial eclipse: when standing in penumbra
shadow
(c) Annular eclipse: when standing beyond the
point of the umbra cone.
Another factor that must be taken into consideration
in the case of Annual and Partial eclipses of
the sun is the fact that both the Earth and Moon
are moving in elliptical orbits rather than circular
orbits. There is also a five degree inclination
in the ecliptic(earth-sun orbit) plane of the
sun vis a vis the moon. This factor is significant
because it determines whether an eclipse will
occur at all – it’s only when the
Moon is moving sufficiently close to the earth
and the radius of the ellipitical orbit of the
moon is minimal that it will cast its shadow,
otherwise the shadow just skims the surface of
the Earth and moves on, without any visible effect
on Earth. The eclipse will be longest when the
moon is closest to the sun and the Sun is farthest
away from it.
The shortest possible Solar eclipse is referred
to as the annular-total eclipse of the sun. The
duration of this eclipse is determined by the
range of the umbra shadow. If this range touches
the surface of the Earth but does not extend beyond
the centre, then this kind of eclipse occurs,
when the light from the sun is obscured for a
few seconds – visible only to those people
who are around the region of the umbra shadow.
OBSERVING A SOLAR ECLIPSE:
The centre of the sun is a region comprising hot
gases, known as the Photosphere. During a total
solar eclipse, this area is completely covered
by the moon. Around the Photosphere, is a circular
ring called chromosphere, which is deep red in
color and appears like a huge mass of boiling
lava as huge masses of boiling gases leap out
into the atmosphere and are sucked back by the
gravity of the sun. They are known as prominences
and during a total solar eclipse, these eruptions
can be viewed as red laser lights around the dark
surface of the moon’s shadow. Surrounding
the chromosphere is the sun’s corona. Depending
upon the level of sun’s activity –
sunspots and storms, the Company will be elongated
or jagged. The sun’s corona covers an area
of about three to six solar diameters from the
moon’s shadow, which causes the light to
disappear rapidly within this area, making it
impossible to photograph. At the northern and
southern ends of the sun, the corona is shorter,
extending out in the shape of brushes and consequently
referred to as Polar brushes.
During a solar eclipse, it is possible to view
the sun with the naked eye, but only during the
brief seconds when the eclipse is total. While
viewing a partial solar eclipse, it is imperative
to use glasses that will filter the sun’s
rays and prevent damage to the eyes. The sun’s
rays, even while in shadow, are strong enough
to permanently destroy the vision of a person
who does not use protective equipment.
LUNAR ECLIPSES:
An eclipse of the Moon occurs when it is in its
full phase and when it passes through a part of
the Earth’s shadow. Such an eclipse occurs
when the earth lies between the sun and the Moon.
Therefore, we may identify the umbra regions (where
all the light from the sun is blocked off) and
the penumbral regions (where the light is only
partially blocked off). Depending upon this factor,
Lunar eclipses have been classified into three
types:
(a) Penumbral lunar Eclipse: when the Moon is
in the Earth’s penumbral shadow
(b) Partial Lunar eclipse; when only a part of
the moon passes into the Earth’s penumbral
shadow. This eclipse can be viewed from the Earth.
(c) When the entire moon passes through the Earth’s
penumbral shadow. The Moon puts on vibrant colours
during this phase.
During the lunar eclipse, a viewer from the Moon
would be able to see the sun as a red ring with
the shadow of the Earth in the middle. On the
Earth however, the Earth’s atmosphere filters
and refracts the rays of the sun, so that the
moon appears to be an interesting plethora of
beautiful colors.
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