十万个为什么·科学阅读30篇（2）
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What Makes Some Snowflakes Form Perfect Hexagons While Others Look Messy?
是什么让一些雪花形成完美的六边形，而另一些却显得杂乱？
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Snowflake symmetry begins with water molecules bonding at 60-degree angles in ice crystals.
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Perfect hexagons form only when temperature stays near −15°C and humidity remains steady for minutes.
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Slight shifts in air pressure or dust particles disrupt molecular alignment during descent.
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Each arm grows identically because vapor diffusion rates match across the crystal’s surface.
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Irregular flakes result from collisions, melting-refreezing, or fluctuating atmospheric layers.
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Scientists use cloud chambers to recreate conditions and photograph real-time growth patterns.
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Microscopic impurities act as nucleation sites, sometimes triggering branched or needle-like shapes.
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Computer models simulate how tiny changes produce vastly different macrostructures reliably.
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Photographing falling snow with high-speed lasers reveals why no two large flakes are identical.
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Studying crystal formation improves weather prediction and aircraft icing safety systems.