The Study of Snowflakes
Snowflakes have long been a subject of mystery and fascination. In 1611, mathematician and astronomer Johannes Kepler published “On the Six-Cornered Snowflake,” the first-known scientific treatise on snow crystals. Philosopher Rene Descartes (famous for “Cogito ergo sum,” or “I think, therefore I am”) also contemplated snowflakes, recording descriptions and drawings of various types of crystals. In 1885, Wilson “Snowflake” Bentley, a self-educated Vermont farmer, became the first person to photograph a single snow crystal by adapting a microscope to a bellows camera. He pioneered the photomicrography of snowflakes, capturing over 5,000 of them on film. His book “Snow Crystals,” first published in 1931, remains in print today. Modern scientists can grow synthetic or “designer” ice crystals in laboratories as they continue to probe the physics behind the formation of snowflakes.
What Is A Snowflake?
A snowflake is not the same as a frozen raindrop or sleet, which occurs when rain passes through a cold layer of air and freezes. Instead, snowflakes begin in clouds as water vapor condenses directly into ice. Although a snowfall may consist of only single ice crystals, sometimes multiple ice crystals combine in the atmosphere. When individual ice crystals join together they make up what is commonly called a snowflake. Snowflakes are more likely to form when the air temperature near the earth’s surface is close to the freezing mark, because at this point the ice crystals are “sticky”, according to Keith C. Heidorn, PhD, who has written numerous books about ice crystals and snowflakes. In below-freezing temperatures ice crystals are much less likely to adhere to each other, which is why snow that falls when it is very cold generally consists only of tiny ice crystals.
Wilson "Snowflake" Bentley (1865-1931), who made photographing snowflakes his life's work.
For centuries, scientists struggled to explain the snowflake’s six-sided form. We now know that a snowflake’s shape is determined at the molecular level, since water molecules form a hexagonal lattice as they crystallize. Small snowflakes take on the shape of a simple hexagonal prism. But under certain meteorological conditions, branches begin to sprout from the corners, leading to more and more elaborate and complex snowflake formations.
"Under the microscope, I found that snowflakes were miracles of beauty; and it seemed a shame that this beauty should not be seen and appreciated by others. Every crystal was a masterpiece of design and no one design was ever repeated. When a snowflake melted, that design was forever lost. Just that much beauty was gone, without leaving any record behind." -- Wilson A. Bentley
Size and Shape
The growth and shape of an ice crystal is affected by the temperature and humidity both inside and outside a cloud. In warmer temperatures ice crystal growth is slowed, while colder temperatures lead to the ice crystal tips becoming sharper. The most complex ice crystals tend to form in high clouds, while middle-height clouds produce the least complex shapes. Low clouds produce a variety of ice crystal shapes. Other factors affecting the size and shape of a snowflake include wind speed, air currents and the amount of dirt in the air. The size of a single ice crystal molecule is usually around 0.02 to 0.20 inches. When ice crystals assemble into a snowflake they usually measure about 0.4 inches, but can potentially grow as large as 1.57 inches. They can grow even larger provided that temperature conditions are ideal and that there is no more than a light wind to buffet the flakes as they fall to earth. The largest snowflake in written history, a whopping 15 inches across, is reported to have fallen in 1887 in Ft. Keough, Montana. More recently, an 8-inch by 12-inch flake was documented in Bratsk, Siberia, in 1971.
Types of Snow Crystals
We most often think of a snowflake as a flat and lacy affair, rather like a wet doily falling from the sky. Not all snow crystals are star-shaped, however. In 1951, the International Commission on Snow and Ice created a simple classification for identifying the seven principal snow crystal types: plate, stellar, column, needle, spatial dendrite, capped column and irregular. Scientists have developed other, more complex snowflake classification systems which subdivide snowflake forms even further. Kenneth G. Libbrecht, a professor of physics at California Institute of Technology who specializes in the physics of crystal growth and pattern formation in ice, states that categorizing snowflakes is akin to classifying dog breeds -- in other words, it is an imprecise science subject to debate.
Stellar dendrites are among the most beautiful and recognizable of snow crystals. Large, flat and star-like, these are the snowflakes of childhood memory and Christmas cards. Taking their name from the Greek word “dendrites” (“pertaining to a tree”), stellar dendrites branch repeatedly during their formation, becoming more and more intricate. These are not the only interesting forms, however -- some snowflakes look like six-sided dinner plates, others like Dorian columns. Some columnar types have hexagonal plates at each end, causing them to resemble cufflinks.
No Two Alike?
We’ve all heard that no two snowflakes are alike. While tiny snow crystals -- simple hexagonal prisms -- can appear quite similar, even under an optical microscope, one complex branching snowflake differs from another in hundreds of ways. Although no one can say for certain that each is unique, the possibility of any two snowflakes being identical is for all practical purposes impossible. A typical snow crystal consists of some 10,000,000,000,000,000,000 water molecules, allowing for a nearly infinite number of snowflake formation possibilities.
California Institute of Technology: SnowCrystals.com
The Weather Doctor: The Joy of Snowflakes
Snowflake Bentley: The Official Website of Wilson A. Bentley (1865-1931)
National Geographic.com: "No Two Snowflakes the Same" Likely True, Research Reveals
The snowflake pictures are from SnowCrystals.com, and were captured by Kenneth G. Libbrecht using a specially designed snowflake photomicroscope. They show real snow crystals that fell to earth in Northern Ontario, Alaska, Vermont, the Michigan Upper Peninsula, and the Sierra Nevada mountains of California.
The picture of Wilson A. Bentley and his snowflake photographs are from Wikimedia Commons and in the public domain.