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 Do
you remember making snowflakes out of paper at school? Well
snowflakes aren’t just for children. They have fascinated
many over the ages including such scientific luminaries as
René Descartes, Robert Hooke, Johannes Kepler, and Antony
van Leeuwenhoek.
Snowflakes form when
atmospheric water is cooled below its freezing point by either
an invasion of cold air, or a sudden updraft into cooler elevations.
The water enters a super-cooled state and snowflake formation
takes place upon air-borne microscopic dust particles acting
as nuclei for condensation. As snow crystals form they take
on a hexagonal shape with an infinite number of variations.
The temperature at
which a crystal forms, and to a lesser extent the humidity
of the air, determine the basic shape. The many things that
happen to snow crystals as they fall, such as collisions,
partial melting and colliding with water drops that freeze
to them, create even more shapes. Irregular crystals with
no easily identifiable form or a combination of more than
one form are the most common, and only 1 per cent of flakes
are thought to be symmetrical.
 Snow
crystals are six-sided because of the shape of the water molecule
which consists of two atoms of hydrogen and one atom of oxygen.
This construction is formed in the shape of a triangle with
three equal sides. When crystallisation takes place, each
new ice crystal bud is formed at an angle of 60 degrees from
the hub or apex of the triangle. Continuing this process,
the hexagon is formed when six of these molecular triangles
are completed and this becomes the framework for further growth.
When it is very cold,
"dry" snow falls - the ice crystals do not stick together
easily, and the snow is fine and powdery. Flakes are small
and their structure is simple. At temperatures nearer to freezing
point, "wet" snow falls and large snowflakes fall, especially
if there is no wind. Individual flakes may be composed of
a very large number of ice crystals (predominantly star shaped)
and flakes may then have a diameter up to several inches.
Large stellar (star shaped) snowflakes may grow to be 5-7
cm (2-3 in) across. The largest snowflakes recorded in the
world fell on 28 January 1887, measuring a mind-boggling 38
cm (15 in) across by 20 cm (8 in) thick, across Fort Keogh
in Montana.
 Details
of their intricate structure can be seen through a microscope
and common types identified include plate (flat), stellar
(star-shaped), column, needle, spatial dendrite (lacy), capped
column and irregular. An American photographer named Wilson
A. Bentley, from Jericho, Vermont USA, was so fascinated by
snow crystals that he amassed a collection of snow crystal
photographs. Nicknamed ‘The Snowflake Man’, he claimed that
he never found two crystals exactly alike.
He spent his life photographing
snowflakes through a microscope and in over forty years from
1885 he took several thousand stunning photographs. He was
quoted in 1925 as saying "Under the microscope, I found that
snowflakes were miracles of beauty; and it seemed a shame
that this beauty should not be seen and appreciated by others.
Every crystal was a masterpiece of design and no one design
was ever repeated., When a snowflake melted, that design was
forever lost. Just that much beauty was gone, without leaving
any record behind."
Useful links
Wilson
A Bentley - The Snowflake Man
Pictures
of snowflakes taken under an electron microscope
Make
a snowflake in a jar
Catching
and studying snowflakes
Virtual
snowflake designer
Paper
directions for making a snowflake
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