The probability that two snow crystals (a single ice crystal) or flakes (a snow crystal or multiple snow crystals stuck together) will be exactly alike in molecular structure and in appearance, is very minute. And to
prove otherwise would not be easy. Each winter there are about
1 septillion (1, 000, 000, 000, 000, 000, 000, 000, 000 or a trillion
trillion) snow crystals that drop from the sky!
To go through all of the snow crystals produced every winter would
be a daunting task. So, we rely on cloud physicists, crystallographers,
and meteorologists to study snow crystals and explain to us why
there are no two snow crystals alike.
First, we need to understand that not all water molecules are
exactly alike. Generally speaking, water molecules have two hydrogen
molecules with one 16O atom. However, not all water
molecules will have this arrangement. Some water molecules will
have an atom of
deuterium in place of one of the hydrogen atoms and some water
molecules will have an atom of 18O. Since the molecular
makeup of snow crystals varies greatly from one to another, it
that each snow crystal will be slightly different.
Furthermore, the unique and complex features of snow crystals
are very much affected by unstable atmospheric conditions. Snow
crystals are sensitive to temperature and will change in shape
and design as they fall from the cloud and are exposed to fluctuating
temperatures. To have two snow crystals or flakes with the same history of
development is virtually impossible.
Back in 2007, new stories flourished that the old adage “No two snowflakes are alike,” might not be true. What these stories were highlighting is that smaller crystals with simple shapes (e.g. hexagonal prisms) may look similar in appearance. The stories also reported that it is possible for snow crystals that have a small number (e.g. 10) of water molecules to be alike (a typical snow crystal contains 1018 water molecules !). As you can tell, depending upon how you define alike or snow crystal you might find two snow crystals that are alike. However, scientific consensus still believes that it is very unlikely for two larger complex snow crystals to be identical in molecular structure and appearance.
Snow Crystal Collection of the Buffalo Museum of Science -
Digital library of Bentley’s original glass slide snow crystal negatives.
Passages from Bentley’s notebook, a bibliography of Bentley’s papers,
and notes on the photographic process are included.
- Cryosphere -
The cryosphere is that portion of the Earth's surface
where water is a solid
form, usually as snow or ice, including sea ice, freshwater ice, snow, glaciers,
and frozen ground (or permafrost). The National Snow and Ice Data Center sponsors
this Web site which has features such as “Cold Facts: Earth's Snow, Ice,
and Frozen Soils” and “State of the Cryosphere.”
do snow crystals form? - Get the science behind snow, from NOAA
- Snowcrystals.com - “This site is all about snow crystals and snowflakes --
what they are, where they come from, and just how these
remarkably complex and beautiful structures are created,
quite literally, out of thin air.”
A. Bentley: The Snowflake Man. Jericho Historical Society -
See Museum link
http://bentley.sciencebuff.org/collection.asp to view a selection of Bentley’s snow crystal images
and take a virtual tour of the museum. Also of interest
are full text articles about or by Bentley under the Resources
more print resources...
Search on "cloud
physics," "ice crystals," "snow crystals," or "snowflakes"
in the Library of Congress Online
Photo courtesy of Kenneth
Photo courtesy of Kenneth Libbrecht
Snowflakes. Horydczak, Theodor, ca. 1890-1971, photographer. Photographer. Prints & Photographs Division, Library of Congress.
Young woman, with basket, walking in snowy country lane. c.1891.
Moran, John Leon. Photographer. Prints & Photographs Division, Library of Congress.