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Kenneth Libbrecht

Author of The Snowflake: Winter's Secret Beauty

11+ Works 929 Members 23 Reviews

About the Author

Kenneth Libbrecht, professor of physics at Caltech, is a world-renowned expert in the science of snow. A North Dakota native, he is the author of Voyageur Press's The Snowflake, The Little Book of Snowflakes, and The Magic of Snowflakes: A Postcard Book.
Image credit: Photo by Steve Ryan (Flickr/Cropped)

Works by Kenneth Libbrecht

Associated Works

New Scientist, 18/25 December 2021 (2021) — Contributor — 1 copy


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Common Knowledge



I already have a Dover book on ice crystals (or I've given it away....I think that's the case) but it was really the work of W A Bentley of Vermont. And the current book is the work of a couple of snow scientists. I was a bit sad to see how they felt that they had to justify their work in the last couple of paragraphs. I feel that it stands on its own as a contribution to knowledge. Certainly the husband and wife team have pulled together some really interesting material about snow crystals and the science behind their formation plus they have produced some really lovely art works from their photos.
I've extracted a few segments from the book that caught my attention, as follows:
We name snowflakes for the same reason we name anything—so we can more easily talk about them. Certain snow crystals are common and distinctive looking, and those have fairly well-defined names. Stellar plates, stellar dendrites, fernlike stellar dendrites, hollow columns, and capped columns have all been part of the snowflake vocabulary for some time. Go significantly beyond that, however, and opinions differ. In an effort to be inclusive, perhaps, tables of snowflake types have become larger with time. In the 1940s the largest classification chart included 41 members. This number jumped to 80 in the 1960s, and recently a new table appeared with 121 different snowflake types. The chart the Libbrechts have produced on p27 shows their preferred snowflake classification. Because there can be no such thing as a final, definitive catalog, thy've pared the number down to make a chart that is convenient for snowflake watching. (It's a temperature cvs humidity chart and I recall seeing something similar in Scientific American many years ago.
Typically, cloud droplets must be chilled to somewhere between 21 degrees Fahrenheit (–6 ° C) and 5 degrees Fahrenheit (–15 ° C) before they turn into ice. Remove the dust, and droplets of very pure water can be supercooled to nearly–40 degrees Fahrenheit (–40 ° C) before they freeze. After it leaves the clouds, the snowflake no longer has a ready source of water vapour, so it stops growing. From then on the crystal drifts slowly downward with a typical velocity of around one mile per hour.
About one hundred thousand cloud droplets provide enough water vapour to make a single snowflake. It depends on how well things are mixed in the atmosphere, but there are probably, very roughly, about a thousand of your molecules captured in every snowflake picture.
The art of snowmaking is now so advanced that you can cover your lawn with white anytime and anywhere, even in summer. Compressed air doesn’t have the cooling power to make summertime snow, but liquid nitrogen freezes those droplets with aplomb.
The hands-down favourite snow inducer comes from the bacterium Pseudomonas syringae. This little beasty produces proteins that nucleate freezing at 28 degrees Fahrenheit (–2 ° C), Scientists were studying the bacterium to better understand and mitigate frost damage on crops. But instead, some clever person realized that this microbe’s talents could be harnessed for making artificial snow. The end result is better skiing at a lower price. You never know where science will take you.

Does it ever snow on other worlds? Possibly, but the snowflakes might look quite different from those found on Earth. On Mars, for example, water ice and carbon-dioxide ice (commonly known as dry ice) have both been spotted, and the latter can be several meters thick at the poles. It is still not known, however, if dry ice falls from the Martian atmosphere as “snowflakes” or forms directly on the surface like frost.

In 1611, Kepler presented a small treatise entitled The Six-Cornered Snowflake to his patron, Holy Roman Emperor Rudolf II, as a New Year’s Day gift. He reasoned that each single plant has a single animating principle of its own, since each instance of a plant exists separately, and there is no cause to wonder that each should be equipped with its own peculiar shape. But to imagine an individual soul for each and any starlet of snow is utterly absurd, and therefore the shapes of snowflakes are by no means to be deduced from the operation of soul in the same way as with plants. Because it was known that cannonballs display a hexagonal pattern when stacked in a pile, Kepler conjectured that these two symmetries might be related. There was a germ of truth in this reasoning, because the geometry of stacking atoms lies at the heart of snow crystal symmetry. But the atomistic view of matter had not been developed by Kepler’s time. the word crystal really comes from quartz and Pliny described clear quartz as frozen ice. Pliny’s misunderstanding is still felt in the language of the present day. If you look in your dictionary, you may find that one of the first definitions for crystal is simply “quartz.” This is like saying the definition of food is “potato.” Funny how some quirks in the language remain after thousands of years.

In the crystal world, there are thirty-two possible ways to stack molecules, including five different cubic forms and seven different hexagonal ones. Some symmetries are forbidden—there are no crystal structures with five-fold symmetry, for example. This is true for the same reason you cannot tile your floor with pentagonal tiles; pentagons simply do not fit together without leaving gaps. In the European Union, “lead crystal” must be composed of at least 24 percent lead oxide, while “crystal glass” must include similar amounts of other metal oxides.

Smooth surfaces are difficult to hold onto, while the rough spots have lots of dangling molecular bonds to grab. As a result, the rough spots accumulate molecules quickly, while the smooth surfaces do so more slowly. Before long, the rough areas add water molecules and fill in, leaving only the smooth areas to define the shape of the crystal. These smooth, slower-moving surfaces become the crystal facets. Faceting is an important player in the genesis of snow crystal structure. Faceting explains the formation of simple hexagonal prisms, defining the snow crystal’s six-fold symmetry. But most snowflakes are much more elaborate than simple prisms, so faceting is only part of the story. The six corners of a snow crystal grow a bit faster because they stick out farther into the humid air, causing branches to sprout. As the crystal grows larger, the same effect causes sidebranches to sprout from the faceted corners of each branch. This process is responsible for the complex shapes of snow crystals. The corners experience runaway growth as this cycle accelerates—the corners stick out a bit, so they grow a bit faster; soon they stick out even more, so they grow faster still. Thus branches sprout from the six corners of a hexagonal prism. This process of runaway growth is called the branching instability, and it is responsible for much of the elaborate structure you see in snowflakes. The six branches all grow independently of one another, but they grow alike because each experiences the same external fluctuations in temperature and humidity. The detailed morphology of each falling crystal is determined by the path it takes through the clouds and by the temperature and humidity it experiences along the way. A complex path yields a complex snowflake. Because no two crystals follow precisely the same path through the turbulent atmosphere, no two snowflakes will be exactly alike. When the ice growth is especially hurried, sidebranches appear rather chaotically as the crystal develops. Chaos and order are both present during snow-flake growth, and this is what makes snowflake patterns so intriguing. By itself, the branching instability brings chaos—the unbridled creation of structural complexity, as exemplified by the random sidebranching in a fernlike stellar dendrite. Faceting, on the other hand, brings order, as embodied by the simple perfection of the hexagonal prism. Bring these two forces together, however, and beautifully intricate, symmetrical snowflakes result.

In terms of mathematically modelling the development of snow crystals, the breakthrough came in 2005 when mathematician Clifford Reiter established that cellular automata models of diffusion-limited growth could produce structures that were both faceted and branched, reproducing many features seen in snowflakes. Subsequent work has demonstrated stellar dendrites, capped columns, hollow columns, double plates, and other snowflake types. The construction of each snowflake reflects a quiet clash between order and chaos that plays out within the winter clouds. We still cannot explain why snow crystals grow into broad stellar dendrites at some temperatures while growing into slender ice columns and needles at other temperatures. Figuring out the interaction of two water molecules is doable, but even state-of-the-art computers cannot handle many molecules at once with sufficient accuracy.

We have no walk-in cold room in our lab; with our chest freezer and all our other snow chambers, we keep the cold boxed up so we can work in room-temperature comfort. Basically our photomicroscope is a set of three microscope objectives covering a range of magni-fications attached to a digital camera using a long extension tube. The objectives are mounted on a custom-built turret, making it easy to change magnifications for different snowflakes. Our specimens are almost always on glass slides, and these rest on a translation stage that moves up and down to focus, as is typical with microscopes Another neat trick for producing laboratory snowflakes is to grow them on the ends of electrically induced ice needles. The basic idea is to use strong electric fields to modify the ice growth behavior, a technique that was discovered in 1963 by Basil Mason and his collaborators at Imperial College London. Ken and his colleagues made some advances in this method

With more than seven billion people on the planet, surely a few of us can be spared to look into these matters. Also, you can rest assured that none of your tax dollars have gone into our snowflake projects.
Well, I liked the book. And I liked their overwhelming honesty about what they knew and what they didn't know. It was refreshing and overall, I found I was quite fascinated with what they were doing. Five stars from me.

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booktsunami | 2 other reviews | Dec 21, 2023 |
An enjoyable look at how snowflakes form and what forms snowflakes can take with a lot of photographs showing the large variety of snowflakes that can exist.
coprime | 4 other reviews | Jan 15, 2023 |
Excellent book including directions on how to make photographs like those in the book. Highly recommended!
lpg3d | Nov 12, 2022 |
The beauty of snowflakes brought to life by the genius of Kenneth Libbrecht.
Huba.Library | 4 other reviews | Oct 29, 2022 |


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