Winter's arrival is always heralded by a pristine, white snow scene. From ancient times to the present, snowflakes have been described using a myriad of poetic metaphors, likening them to delicate crystals of salt, sugar, or goose feathers.

Yet, if one observes closely, it becomes apparent that most snowflakes exhibit a six-petal shape. Why do snowflakes form this particular shape? What scientific principles underlie their formation?

Snowflakes are formed through the growth of ice crystals. These ice crystals are solid hydrates created by the condensation of water vapor onto ice nuclei, which can be considered the early form of snowflakes.

The process of snowflake formation resembles a delicate "race," in which the growth of ice crystals is influenced by temperature and humidity.

As early as the Western Han Dynasty, people recognized the pattern that snowflakes are predominantly six-petaled. Modern technology has allowed us to observe this phenomenon more clearly.

Ice crystals belong to the hexagonal crystal system, characterized by four crystal axes: one main axis and three auxiliary axes. The main axis is perpendicular to the base plane, while the auxiliary axes intersect at an angle of 60 degrees.

The growth mode of ice crystals determines the shape of snowflakes. When the main axis grows faster than the secondary axes, the ice crystals form columns, creating a structure known as "needles."

Conversely, when the main axis grows slower than the secondary axes, the ice crystals take on a flake shape, referred to as "lamellae." This growth mechanism results in most snowflakes being hexagonal because, under these conditions, the main axis grows more slowly, leading to the formation of a hexagonal basic shape.

Temperature and humidity play crucial roles in the growth of ice crystals. At very low temperatures, the growth of ice crystals is inhibited, leading to the formation of small snow crystals. When the temperature approaches 0°C, the base of the snowflakes is predominantly hexagonal.

Humidity also significantly impacts the shape of ice crystals. At low humidity, ice crystals grow slowly, forming columns or needles. In contrast, high humidity accelerates the growth of ice crystals, resulting in complex star-shaped snowflakes. These variations cause snowflakes to exhibit a diverse array of shapes during their descent.

Snowflakes can merge during their fall. As they descend, snowflakes may collide, rub against each other, or even stick together, forming larger snowflakes. This merging phenomenon can result in very large snowflakes.

Beyond their visual beauty, snowflakes hold significant value in scientific research. They are often termed "messengers from the sky," as scientists can infer atmospheric conditions by analyzing the crystal forms of snowflakes.

Furthermore, the study of snowflakes has contributed to advancements in atomic physics and positively impacted research in drug molecules, semiconductor chips, and solar cells.

The formation of snowflakes is a process replete with both aesthetic beauty and scientific intrigue. From the intricate structure of ice crystals to the diverse forms of snowflakes, these natural phenomena inspire awe and reveal the wonders of nature.

Snowflakes, akin to a group of whimsical elves, adorn our world while embodying profound scientific knowledge waiting to be explored and understood.