by Knut Jørgen Røed Ødegaard
During a solar eclipse a whole range of strange phenomenons can be
experienced. Here you'll learn a little about these and how to
experience these phenomenons.
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Below a leaf-covered treetop hundreds or thousands of partially
obscured suns will be visible during a solar eclipse. The photo was
taken on August 11th 1999 in Austria when approximately 70 % of the
Sun was hidden behind the Moon
Photo: Oddleiv Skilbrei |
SUNSPOTS
If the weather is decent we may be able to see sunspots - dark areas
on the Sun. The spots appear dark because they're cooler than the rest
of the surface of the Sun - the temperature is approximately 4500
degrees versus 6000 degrees on the surrounding surface. The spots are
due to very strong magnetic fields - they're many, many times stronger
than the Earth's magnetic field. Even spots not appearing particularly
large in a telescope are larger than the Earth in area! The Sun is
gigantic!
The amount of sunspots varies with a periodicity of around 11
years. Lately there have been few spots, but the number will probably
increase towards the eclipse. The magnetic fields causing the spots
also cause violent eruptions on the Sun. These eruptions cause Aurora
Borealis, the Northern Light, here in the north.
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From time to time there are many small and large
sunspots on the solar disk. During the eclipse we may
experience these, please refer to observations of the
eclipse.
Photo: SOHO/ESA/NASA
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PROJECTIONS OF THE SUN BELOW TREES
Under leaf-covered trees strange half moon- or sickle-shaped
projections of the Sun are created. These can be seen if you find a
good place with suitably dense leaf-covered trees. It's good if the
leaves are medium large and the tree should be dense enough to let the
light pass partially through. The ground must be of a quality which
will easily show the projections. Light asphalt, concrete pavers or
wooden surfaces are ideal.
Notice how the projections will change when the Sun becomes
increasingly obscured and how they change again when the Moon
withdraws.
SILVER COLOURED LIGHT
When the eclipse is considerable (there's no exact limit, but say 50
%), the light will become more and more subdued and silver
coloured. This is due to the intense and direct light from the solar
disk decreasing in strength and thereby the light from the strange
solar corona will become more noticeable.
The sunlight comes from the Sun's visible surface which has a
temperature around 6000 degrees. This layer is called the Sun's
photosphere. Outside the photosphere there is an atmospheric layer
with considerably lower density. The innermost layer is the
chromosphere which at the bottom is cooler than the photosphere. In
the top layer of the chromosphere the temperature rises quickly and in
the layer surrounding the chromosphere, the corona, the temperature is
above one million degrees. One would expect a gas at more than one
million degrees would radiate amazingly strongly. But the corona
doesn't do that!
The reason is that the gas in the corona has very low density. As seen
from the Earth the corona is strongly dominated by the Sun's visible
surface. Only during total solar eclipses can we see the corona from
the ground. But during partial eclipses a part of the sunlight is
obscured which leaves the corona's superhot, silver shimmering light
visible.
The eclipse on August 1st is large enough for us to expect this effect
to become noticeable in the north. At the same time the sunlight is
obscured and it will become darker.
PHOTOS TAKEN DURING THE TOTAL SOLAR ECLIPSE IN THE SOUTH OF AFRICA IN
2001
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Early in the partial phase the eclipse has no effects visible to the
naked eye (except with solar eclipse glasses on the solar disk
itself). But after some time several interesting and fascinating
phenomenons appear. The photo shows how the openings in the leaf cover
on a tree create many images of the partially obscured Sun. Instead of
the usual diffuse spots of light, there are now "half suns" on the
ground. The eclipse is here well above 50%.
Photo: Herman Ranes |
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When the eclipse reaches 90-95% it becomes clearly noticeable that
there's less light. The shadows become razor sharp since the sunlight
now originates from a point source in the sky. The photographer has
captured his own shadow.
Photo: Herman Ranes |
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When the eclipse is descending, the thin solar disks are positioned in
the opposite of their direction before the maximal phase.
Photo: Herman Ranes |
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