There are many different snowflake shapes. At the heart of every snowflake is a tale of molecular architecture, atmospheric conditions, and the symphony of physics and chemistry. Let’s delve into the captivating world of snow crystals and explore how and why they assume their myriad shapes.
- Most snowflakes are hexagons or six-sided shapes.
- Temperature and humidity affect snowflake shapes. Certain shapes only occur at very cold temperatures.
- There are at least 30 different shapes of snowflakes, but all depend on the same geometry.
How Do Snowflakes Get Their Shape?
Snowflake shapes come from the molecular structure of water (H2O). A water molecule consists of two hydrogen atoms bonded to one oxygen atom, forming a V-shape with an angle of about 104.5°. When these molecules solidify or freeze, they form a hexagonal lattice due to electrostatic repulsion and hydrogen bonding. The hydrogen “arms” of each molecule carry positive electrical charges. Since like charges repel, the arms maximize the distance between them. Similarly, oxygen atoms repel each other due to their like charge. At the same time, the partial negative charge on an oxygen atom attracts the hydrogen atoms of other water molecules. The balance of charges produces a hexagonal shape, which is the foundation for the six-sided symmetry observed in most snowflakes.
Nuclear Sites: The Birth of a Snowflake
Snowflakes start as supercooled water droplets in clouds. These droplets need a nucleus, like a dust particle or another impurity, around which they can freeze. This is a process known as nucleation. Once initiated, crystallization proceeds as water molecules arrange themselves according to the hexagonal pattern.
The Role of Temperature and Humidity
The ultimate shape of a snowflake depends mainly on temperature and humidity (water vapor availability):
- Temperature: Snowflakes are crystals of water ice. They form at temperature at or below the freezing point of water. Different freezing temperatures promote the growth of specific facets on the forming crystal. Also, snow crystals experience temperature gradients on their journey toward the ground, sometimes partially melting and re-freezing. Because the process is complex, no two snowflakes are quite alike. However, snowflakes often look similar to each other when they fall under the same conditions.
- Humidity: High humidity levels mean more water vapor is available for deposition, influencing the rate and nature of crystal growth. So, some snowflakes are larger than others.
List of Snowflake Shapes
How many snowflake shapes there are depends on who you ask. Wilson Alwyn Bentley photographed thousands of snowflakes and placed them into 35 different categories. Ukichiro Nakata also photographed snowflakes and devised a classification system of 41 snow crystal types. Nakata made the first artificial snowflakes, too.
Here is a list of some of the most noteworthy snowflake shapes and the conditions under which they form:
- Hexagonal Plates: Flat, six-sided crystals that form in temperatures between -2°C and -15°C. They grow primarily in lower humidity conditions.
- Stellar Plates: Six-branched stars with broad arms. They grow in similar conditions to hexagonal plates but with higher humidity.
- Stellar Dendrites: These are star-shaped snowflakes with elaborate, feathery arms. They form in high humidity at temperatures between -12°C and -16°C.
- Fernlike Stellar Dendrites: Even more intricate than stellar dendrites, these have complex, fern-like branches. They form under the same conditions as stellar dendrites but require higher humidity levels.
- Twelve-branched Snowflakes: Occasionally, two snowflakes meld at a 30° angle, producing a twelve-branched flake.
- Triangular Crystals: These rare shapes form at temperatures just below -2°C. Instead of the usual hexagonal symmetry, certain conditions promote a three-fold symmetry. They look like hexagonal plates and do have six sides, but three sides are long and three are short, producing an overall triangular appearance.
- Needles: Thin and long, they appear when temperatures hover between -3°C and -8°C.
- Columns: Cylindrical in shape, these form in temperatures between -6°C and -10°C and again between -22°C and -27°C.
- Bullets: Essentially two column crystals fused side by side, formed in similar conditions as columns.
- Diamond Dust Crystals: Tiny, clear crystals that form in clear, cold conditions often seen in Antarctica or during cold, clear nights. These crystals include tiny flat hexagons and also more three-dimensional columns.
- Rimed Crystals: These have a frosty appearance due to supercooled water droplets colliding with a snow crystal and freezing on its surface. Any of the shapes occurs with rime if the conditions are right. Rime photographs as tiny beads on the otherwise smooth surface.
- Irregular Shapes: As the name suggests, these do not have a defined shape and are the result of random collisions and fusions or melting and refreezing.
Observe and Photograph Snowflakes With Your Phone
Capturing the ephemeral beauty of snowflakes is a rewarding experience. While Bentley and Nakata needed special cameras and microscopes, modern phones do macro photography with ease!
- Charge your phone. Batteries run down more quickly when it’s cold.
- Use a dark-colored material as a background. Black or dark velvet or wool works great, but even dark paper works. Make sure it gets cold before you start catching snowflakes, or else they will melt before you can get a picture.
- Find a calm location, since wind carries away snow before you can photograph it. Catch snowflakes or let them fall onto the dark background.
- Now, zoom in. If you have a separate macro mode, use that. Ideally, use a tripod with your phone so there is no shakiness. Many phones also have image stabilization built in. Natural lighting works in the day, but if it’s dark, use a flashlight angled to the side for indirect lighting.
- After you take your photo, crop out unnecessary parts of the image. Adjust the contrast and brightness so the snowflake stands out against the background.
- Bailey, Matthew; Hallett, John (2004). “Growth rates and habits of ice crystals between −20 and −70C”. Journal of the Atmospheric Sciences. 61 (5): 514–544. doi:10.1175/1520-0469(2004)061<0514:GRAHOI>2.0.CO;2
- Bentley, Wilson A.; Humphreys, William J. (1931). Snow Crystals. New York: McGraw-Hill.
- Bishop, Michael P.; Björnsson, Helgi; Haeberli, Wilfried; Oerlemans, Johannes; Shroder, John F.; Tranter, Martyn (2011). Singh, Vijay P.; Singh, Pratap; Haritashya, Umesh K. (eds.). Encyclopedia of Snow, Ice and Glaciers. Springer Science & Business Media. ISBN 978-90-481-2641-5.
- Harvey, Allan H. (2017). “Properties of Ice and Supercooled Water”. In Haynes, William M.; Lide, David R.; Bruno, Thomas J. (eds.). CRC Handbook of Chemistry and Physics (97th ed.). Boca Raton, FL: CRC Press. ISBN 978-1-4987-5429-3.
- Nakaya, Ukichiro (1954). Snow Crystals: Natural and Artificial. Harvard University Press. ISBN 978-0-674-81151-5.