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SnowflakeA snowflake is a uniquely shaped piece of falling snow, a crystalline form of water ice.
GeometryAn interesting question is why the arms of snowflakes are symmetrical, and why no two snowflakes appear to be identical. The answer is believed to be due to the fact that the distances between snowflakes are much greater than the distances across snowflakes. Given the initial six-fold symmetry from the crystal structure of ordinary ice (known as ice Ih), the arms of a snowflake grow independently in an environment that is believed to be rapidly varying in temperature, humidity and so on. This environment is believed to be relatively spatially homogenous on the scale of a single flake, leading to the arms growing to a high level of visual similarity by responding in identical ways to identical conditions, much in the same way that unrelated trees respond to environmental changes by growing near-identical sets of tree rings. The difference in the environment in scales larger than a snowflake leads to the observed lack of correlation between the shapes of different snowflakes. However, the concept that no two snowflakes are alike is incorrect: it is entirely possible, but unlikely, that a pair of snowflakes may be visually identical if their environments were similar enough, either because they grew very near one another, or simply by chance. The American Meteorological Society has reported that matching snow crystals were discovered by Nancy Knight of the National Center for Atmospheric Research. The crystals were not flakes in the usual sense but rather hollow hexagonal prisms.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Snow" and from http://www.white-on.com
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