THE SOUTHWORTH PLANETARIUM
207-780-4249       www.usm.maine.edu/planet
70 Falmouth Street  Portland, Maine 04103
43.6667° N,                    70.2667° W
Founded January 1970
         "The Universe creates because it can."





THE DAILY ASTRONOMER
Wednesday, December 30, 2015
Snowflake Astronomy

Gathered in piles, they appear rather unremarkable.   White,
indistinct and, when lifted en masse, are far more burdensome than
beguiling.    Yet, if closely observed in isolation, the snowflake is
seen as pure artwork.   A unique and elegant configuration of ice
crystals arranged hexagonally.    As innumerable crystals comprise
each flake, trillions upon trillions of different patterns are
possible.   Hence, the adage, "no two snowflakes are alike."

See a few snow flake close ups on the Daily Astronomer Image Page:

http://usm.maine.edu/planet/december-30-snowflake-astronomy

Today's DA discusses the "astronomy" of snowflakes.    We realize that
one has to stretch the definition of "astronomy" and then leave it
draped over a porch banister for a night to make it relate to
snowflakes.  However, now that the snow has finally arrived, we wanted
to seize this opportunity to celebrate and explain the gorgeous
spectacle of the snowflake.  Why is their shape hexagonal?    Why are
their shapes unique?


The first requirement for a snow flake to form is nucleation.   A
frozen water droplet must attach itself to a dust or pollen particle.
 After it accumulates sufficient amounts of ice, the weighty nucleus
descends through the atmosphere and collects other droplets during the
fall.  This prolonged descent is chaotic.  No two paths are the same,
hence the snowflake's uniqueness.     Ice collects along six "spokes"
radiating away from the center.   This hexagonal design reflects the
water molecule's internal structure.  Like a fractal that infinitely
replicates the same pattern, a snowflake is a macroscopic reproduction
of a microscopic configuration.

Apart from the falling flake's pathway, another variable is
temperature and humidity, both of which change during the descent.
 Warmer sub-freezing conditions, around 25 degrees F, produce
needle-like arms, whereas colder air around 0 F tend to produce
plate-like crystals.       Even though a snowflake's local conditions
change during its formation, at any given moment, the conditions along
a single, small snowflake are constant, so the flake will always
exhibit an elegant symmetry, as evidenced by the images shown within
the link above.

As they consist of ice, snowflakes are clear. We perceive them as
white because they reflect light back to us.    Consequently, freshly
fallen snow appears almost blindingly bright under sunlight.

A single snow storm can produce countless snowflakes, the vast
majority of which go unobserved.    They are tucked under shrouds or
create the glittering membrane of vast snow fields.   The delicate
structures and complex crystals sculpted by Earth's winds remain
unknown and therefore unappreciated.       We know, however, that
embedded within all snow piles are myriad miracles of natural sorcery.