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If you ever find yourself gazing at falling snow, why not catch a few snowflakes on your glove and examine their shapes?
当你凝视着飘落的雪花，为什么不试着用手套接住几片并观察它们的形状？
You might notice that they look symmetrical, and if you look closely, you'll see they have six sides.
你可能会发现它们看起来是对称的，当你近距离观察，你会发现它们有六个面。
You could say a snowflake is simply frozen water,
你可以简单将雪花定义为冻住的水，
but compare one with an ice cube from the freezer, and you'll realize they're very different things.
但与冰箱制造出的冰块相比，你会发现它们其实有着天壤之别。
Unlike ice cubes, formed when liquid freezes into a solid,
不像从液体凝固成固体的冰块那样，
snowflakes form when water vapor turns straight into ice.
雪花直接由水蒸气凝华成冰。
But that still doesn't explain why snowflakes have six sides.
但这仍旧不能解释为什么雪花有六个边。
To understand that, we need to delve deeper into the physics of water.
为了更好地理解这个问题，我们需要更深入地研究水的物理性质。
Water is made out of two hydrogen atoms and one oxygen atom.
水分子由两个氢原子和一个氧原子构成。
A single water molecule thus has ten protons and ten electrons, eight from oxygen and one from each hydrogen atom.
因此一个水分子有十个质子和十个电子，其中八个来自氧原子，剩下两个分别来自两个氢原子。
The two electrons from oxygen's outer shell are shared with two electrons from both hydrogens as they bond together,
来自氧原子外壳的两个电子通过分享分别来自两个氢原子上的两个电子，使氢原子和氧原子键合在一起，
and the remaining four outer shell electrons from oxygen form two pairs.
氧原子外壳上剩下的四个电子分别组成两对。
We call the bonds between these atoms covalent bonds.
我们将这些原子之间的键称作共价键。
The pairs of electrons are all negatively charged.
每对电子都带负电荷。
Similar charges repel, so they tend to stay as far away from each other as possible.
异性相斥，所以它们倾向于距离对方尽可能地远。
The pairs form four electron clouds, two of which are where the hydrogen and oxygen share electrons.
这几对电子形成四个电子云，其中两个来自氢原子和氧原子共享的两对电子。
The repulsion between the unbonded pairs is even stronger than repulsion between the shared pairs,
剩返的两对电子之前的斥力比共享电子对之间的斥力更强，
so the two hydrogens get pushed a little further to an angle of 104.5 degrees.
所以两个氢原子被推得更远，形成一个104.5度的角。
The water molecule as a whole is electrically neutral, but oxygen gets a larger share of electrons,
水分子整体呈电中性，但氧原子分享到更多的电子，
making it slightly negative and the hydrogens slightly positive.
使得氧原子带负电荷而氢原子带正电荷。
Due to its negative charge, the oxygen in one molecule is attracted to the positive charge of the hydrogen in another molecule.
由于氧原子的电负性，一个水分子里的氧原子会被另一个水分子里带正电荷的氢原子吸引。
And so a weak bond between the two molecules, called a hydrogen bond, is formed.
所以两个分子间的弱键，我们称之为氢键的键，就形成了。
When water freezes, this bonding occurs on repeat,
当水结冰，这样的键合不断重复，
ultimately forming a hexagonal structure due to the angle between hydrogens and oxygen within each molecule.
由每个水分子内氢原子和氧原子的角度驱使，最终形成一个六边形结构。
This is the seed of a snowflake, and it retains a hexagonal shape as it grows.
这就是雪花的种子，并在雪花的形成中始终保持六边形的形状。
As the snowflake moves through the air,
当雪花在空气中移动，
water vapor molecules stick to the six sharp edges and expand the snowflake outwards, bit by bit.
水蒸气分子黏合在六个锋利的边缘，使雪花向外一点一点扩大。
A snowflake's developing shape depends on atmospheric conditions, like humidity and temperature.
雪花的形状发展取决于大气条件，如湿度和温度。
As a snowflake falls, changes in weather conditions can affect how it grows,
当雪花飘落，大气条件的变化会影响到雪花如何生长，
and even small differences in the paths two snowflakes take will differentiate their shapes.
即使是两片雪花飘落路径中极微小的差异也会使它们的形状有所不同。
However, since conditions at the six sharp edges of one snowflake are similar, a symmetric snowflake can grow.
然而，由于雪花六个锋利的边缘是相似的，雪花会生长为对称的形状。
Weather conditions affect snow on the ground, as well.
天气状况也能在地表影响雪的状态。
Warmer ground temperatures produce a wetter snow that is easier to pack
温暖的地表温度帮助形成湿润瓷实的雪，
because liquid water molecules help snowflakes stick to each other.
因为液态水分子帮助雪花互相粘连。
Melted snow also plays a critical role in another wintry activity, skiing.
融化的雪同样在另一个冬季活动--滑雪中起着至关重要的作用。
Completely dry snow is very difficult to ski on
在干燥的雪上滑是非常困难的，
because there's too much friction between the jagged snowflakes and the ski surface.
因为锯齿状的雪花和滑雪板之间的摩擦力太大了。
So what's happening is that as skis move, they rub the surface of the snow and warm it up,
所以事实上随着滑雪板的移动，雪的表面温度由于摩擦而升高，
creating a thin layer of water, which helps them slide along.
形成一层薄薄的水帮助其滑动。
So technically, it's not really snow skiing, but water skiing.
因此从技术上讲，这不是真正的滑雪，而是滑水。
But it is true that no matter how hard you look,
但无论你多仔细地观察，
you're almost definitely not going to find two identical snowflakes,
你几乎一定不会找到两片相同的雪花，
and that's a mystery that scientists are still trying to solve,
这是一个科学家们仍在试图解决的谜团，
though we know that it has to do with the many possible branching points in snowflake formation, and the differences in temperature and humidity,
尽管我们知道这与雪花形成中的众多分支点，以及温度和湿度的差异相关，
and while we wait for the answer, we can enjoy watching these tiny fractals falling from the sky.
而在等待答案的时候，我们不妨尽情欣赏这些微小的不规则碎片在空中寂静飘落。
