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Macro photography of a natural snowflake. A snowflake is a single ice crystal that is large enough to fall through the Earth's atmosphere as snow. [1] [2] [3] Snow appears white in color despite being made of clear ice. This is because the many small crystal facets of the snowflakes scatter the sunlight between them. [4]
The two hydrogen atoms bond to the oxygen atom at a 105° angle. [3] Ice crystals have a hexagonal crystal lattice, meaning the water molecules arrange themselves into layered hexagons upon freezing. [1] Slower crystal growth from colder and drier atmospheres produces more hexagonal symmetry. [2]
Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets, which freeze in hexagonal-shaped crystals. Snowflakes take on a variety of shapes, basic among these are platelets, needles, columns and rime. As snow accumulates into a snowpack, it may blow into drifts.
The hexagonal snowflake, a crystalline formation of ice, has intrigued people throughout history.This is a chronology of interest and research into snowflakes. Artists, philosophers, and scientists have wondered at their shape, recorded them by hand or in photographs, and attempted to recreate hexagonal snowflakes.
An early classification of snowflakes by Israel Perkins Warren. [2] Snow was described in China, as early as 135 BCE in Han Ying's book Disconnection, which contrasted the pentagonal symmetry of flowers with the hexagonal symmetry of snow. [3] Albertus Magnus proved what may be the earliest detailed European description of snow in 1250.
In the best-known form of ice, ice I h, the crystal structure is characterized by the oxygen atoms forming hexagonal symmetry with near tetrahedral bonding angles. This structure is stable down to −268 °C (5 K; −450 °F), as evidenced by x-ray diffraction [ 5 ] and extremely high resolution thermal expansion measurements. [ 6 ]
In the hexagonal family, the crystal is conventionally described by a right rhombic prism unit cell with two equal axes (a by a), an included angle of 120° (γ) and a height (c, which can be different from a) perpendicular to the two base axes. The hexagonal unit cell for the rhombohedral Bravais lattice is the R-centered cell, consisting of ...
D n consists of n rotations of multiples of 360°/n about the origin, and reflections across n lines through the origin, making angles of multiples of 180°/n with each other. This is the symmetry group of a regular polygon with n sides (for n ≥ 3 ; this extends to the cases n = 1 and n = 2 where we have a plane with respectively a point ...