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Light
Pillars
An Introduction to Sun Pillars and Related Phenomena.
The BBC is not responsible for the content
of external websites. |
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| FACTS |
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Ice
crystals form in a wide variety of shapes and sizes: stars,
needles, columns and plates.
When
bright light passes from the sun, moon or an artificial light
source through a portion of the sky containing a concentration
of ice crystals, magical apparitions often appear.
The
crystals focus, scatter, bend, split and reflect the light rays
into a kaleidoscope of optical phenomena: arcs, glories, halos,
pillars and sun dogs. |
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Ice
crystals form in the atmosphere in a wide variety of shapes and
sizes and when bright light from the Sun, Moon or even a street
light passes through a part of the sky containing them, some interesting
shapes develop.
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| As
the sky begins to lighten the Upper Sun Pillar changes too |
One
of these is the Light Pillar and the most commonly seen form is
the Upper Sun Pillar. It extends from 5 to 10 degrees above the
sun when it is just below or just below the horizon.
The
ice crystals are in the form of flat hexagonal plates and these
reflect the light externally and internally downwards. When the
crystals are below a line between the observer and the sun they
can reflect the light upwards to form a pillar that appears to be
under the Sun.
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| The
Sun rises in west Cornwall. The beam of light above is the remains
of
the Upper Sun Pillar. |
Because
the light forming the pillar is reflected, the pillar takes on that
colour so that it is red or orange when close to the horizon and
becomes yellow or white as the sun rises.
This
change can be seen in the pictures on this page.
They
were all taken around dawn on Sunday 16th of May 2004, one by Amanda
Jenkin and the others by BBC Radio Cornwall's Chris Stumbles.
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