Snow flower: The miraculous creation of nature

Do you know why snowflakes have very complex shapes but are perfectly symmetrical? And do you know that no two snowflakes are exactly the same? Let's learn about the physics of snowflakes!

The miraculous creation of snow flowers

Surely one of us has seen pictures of paper snowflakes stuck on decorative walls during the winter festival. The size of each snow flower is only 1 mm, the hexagonal symmetrical shapes are very complex but also perfect, maybe there are snowflakes like this really?

The crystal structure of water in solid form

Solid water has a hexagonal crystal structure . Figure 1 depicts ice crystals under different angles, in which red dots represent oxygen molecules, and gray hyphens are hydrogen atoms. Because the water has a molecular formula of H2O, so each oxygen atom has two hydrogen atoms. It is the hexagonal symmetry of solid water crystals that makes snowflakes have hexagonal symmetry.

Figure 1: Crystal structure of solid water.(Photo: Gwdg.de)

You may ask: if so, then I wish in the refrigerator to solidify into a solid, why is it not as symmetrical as snow flower?

Because the water in the refrigerator changes from liquid to solid , snow flowers are formed when the water moves directly from the vapor to the solid (condensed steam into snow flowers - this process takes place in the clouds). . That's why snowflakes are symmetrical, while ice is not.

Figure 2: Cube crystals tend to fill in imperfections (there are unfinished links) until all surfaces are flat.The same thing happens with hexagonal crystals of water.

You can argue: But the hexagonal symmetrical structure of solid water crystals (at the micro level) is unlikely to create the hexagonal symmetrical structure of snow flowers (at the macro level), Just like if you randomly gather multiple hexagonal blocks, it is unlikely that you will have a large hexagonal block.

To clarify this, let's take a closer look at the process of forming a snow crystal . Initially, a group of water molecules randomly mix together, forming a crystal with a rough surface. In such rough places, the water-bonding bonds are not yet filled (ie, the gray hyphen in Figure 1 is broken in many places but not closed into hexagons). Then, the water molecules that come later tend to fill those seats to complete broken connections, until all the surfaces are flat. Figure 2 illustrates this process with quadrilateral symmetry crystals. Similarly, hexagonal symmetrical water crystals will form ice crystals that also have hexagonal symmetry.

At this point, we only understand why the snow crystal has hexagonal symmetry . The next section will explain the creation of sophisticated, sophisticated patterns of snowflakes.

Figure 3 depicts the process of forming a snow flower . As explained above, when tiny ice particles combine, they form a hexagonal symmetrical cylinder (step 2 in the diagram in Figure 3). As these cylindrical crystals become bigger and bigger, they ' grow ' with 6 branches from 6 vertices of the hexagon. The cause of this branch development is as follows: On a cylindrical crystal, the peaks protrude more than the rest. Therefore, the peaks are the place to receive crystal crystals to enter into large crystals rather than other parts. As a result, these vertices grow faster than the rest, forming branches growing from the vertices. These branches are also hexagonal cylinders (because they are also ice crystals), so they develop extra branches due to the same cause as above. Then the sub-branches grow branches again, and go on. This process creates the complexities of snowflakes, and also explains why the branches of snowflakes have a tree-like appearance.

Figure 3: Diagram illustrating the process of forming a snow flower.(Photo: LiveScience)

Here, the last (and also very interesting) thing to explain is why the six branches of a snow flower are almost exactly the same, while it is impossible to find two completely identical snowflakes . In the process of branches being formed the crystal moves relentlessly in the cloud, to places with temperature and humidity (the two most important factors that determine the shape of snowflakes - will be mentioned shortly after). ) different. However, because the crystals are so small, no matter where it goes, the crystal still has the same temperature and humidity, and therefore the branches grow evenly, forming shapes. same in all 6 branches. And also because the crystals move randomly, there are no two crystals under the same conditions of temperature and humidity. As a result, no two snowflakes are exactly alike.

Depending on the temperature and humidity conditions of the air where snowflakes are made up, snow flowers will have different shapes. The morphological diagram below shows the shape of the snow flower corresponding to its formation.

For example, snowflakes in thin discs and star-shaped snowflakes are formed when the temperature is about 2 degrees Celsius, while rods and needles form near -5 degrees Celsius. At about -15 degrees Celsius, snow flowers Disc type and star form reappear. The mixture of disk and rod snow is formed when the temperature is about -30 degrees Celsius. Also from this chart, we realize that the higher the moisture content (the more towards the top of the chart), the snow flower is formed. The more complex and vice versa. The snow flower is long and the disk is formed when the humidity is very high (nearly 100%).

Figure 4: Morphological diagram of snow flower.(Photo: Pandasthumb.org)

Snow formation

Why is snow white? Is there any other color?

Snow is white. It is well known, so obvious, that people use snow as a standard for white (' snow-white '), and ancient tales also have Snow White. But, have you ever wondered why snow is white? And is there any other color?

Snow flower itself is a transparent crystal , like glass. However, a whole bunch of snow crystals together will be white, just as if you crushed the glass, it will be white. The physical cause of this is as follows. The incident light ray is partially reflected on the surface of the snow crystal. When there are so many surfaces, light rays are reflected many times and can even be scattered back. Most monochromatic light is scattered quite well, so we see white snow.

In fact, light rays are also partially absorbed when they reflect back and forth between surfaces, in which red light is absorbed more strongly than blue light. Experiments show that light with a wavelength of about 470 nm (between green and blue) is least absorbed. So, if you dig into a layer of snow, you can see that the snow is blue .

Some pictures of snow flowers. (Photo: Newsfromrussia.com)