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Kenneth G. Libbrecht talks about why he became interested in snow, the physics behind snow crystals, ...
2021-02-17 09:00:00

In Search of the Perfect Snowflake
An Interview with Kenneth G. Libbrecht

Photo by Kenneth G. Libbrecht
In Search of the Perfect Snowflake
In Search of the Perfect Snowflake

Kenneth G. Libbrecht is a professor of physics at the California Institute of Technology. For 20 years, he has been studying crystal growth and the formation of snowflake shapes. He studies snow not only from a scientific point of view, but also tries to catch its elusiveness – by taking pictures of snowflakes. He has published seven richly-illustrated books. Katarzyna Rodacka talked to Libbrecht about snowflakes, and the magical and physical properties of snow.

Read in 8 minutes

Katarzyna Rodacka: Snow is quite a niche hobby. Where does such a hobby come from?

Kenneth G. Libbrecht: It all started with physics. At university we studied crystal growth. I just found it interesting to see how snowflakes grow and from where all these beautiful crystal shapes come. As a child, I didn’t really look at snow carefully. But in my scientific life, I started to notice how interesting this phenomenon is.

Do we already know how a snowflake grows?

People have been trying to understand this for many decades, but many facts remain unknown. It is known that it is a process of building up molecules. To learn a bit more about it, I had to grow my own snowflakes in the lab. Thanks to this, I can measure how quickly snow crystals grow and on what kind of conditions this growth depends. And further – I can design and create my own snowflakes.

What conditions do these beautiful snowflake shapes depend on?

It’s quite complicated. Already in the 1930s, it was discovered that snow crystals sometimes build thin, flat structures; sometimes they create shapes similar to columns (or perhaps a better comparison would be a pencil). Their structure depends on the temperature. When it is cold, snowflakes are flat; as it gets colder, snowflakes take the shape of columns; as it gets even colder still, the snowflakes become flat again. And if it becomes colder yet again? Columns fall from the sky.

Photo by Kenneth G. Libbrecht
Photo by Kenneth G. Libbrecht

So it is temperature that has the biggest impact on them?

It all depends on the temperature, humidity and air pressure. The humidity must be above 100% and the temperature, of course, must be below zero degrees Celsius. In the laboratory, we can create conditions that differ significantly from atmospheric ones. We can create a very high humidity, in which the snowflakes will grow very quickly and will create very complex shapes.

What can these discoveries bring to mankind?

They don’t have any application. People usually grow crystals because it can be useful in the development of technology. Studying snow crystals is pure science. I want to understand this phenomenon.

Do many people across the globe study snow crystals?

A handful of people. My team is just me. I have been studying this topic for 20 years; sometimes some students help me during summer internships. In parallel with my research, I also started taking pictures of snowflakes and observing snow crystals, which is quite an eccentric hobby when you live in Southern California – where it never snows. But for photography, I travel to Alaska or the north of Canada.

What exactly do you research in your scientific work?

I’m interested in the phenomenon of how molecules stick to surfaces. This is quite difficult to study, because the molecules move too fast. In the laboratory, I usually build a snowflake and shoot a video under a microscope. The process itself is not too complicated in terms of the technologies that need to be used. It is, however, difficult from the point of view of physics. We don’t know how the crystals grow. Crystallography, for example, deals with a model of the structure of stable crystals. It is much more difficult to study growth, because growth is movement, not a stable model.

How long has your area of research been going on for?

Kepler was already observing snow in 1611. He noticed that each snowflake is a symmetrical hexagon. He wondered why they has six sides, and not eight or four. People had probably noticed it before, but it was Kepler who first defined it as a scientific observation that could be a prelude to scientific research. He was not able to study snow further, because at the beginning of the 17th century, people didn’t know about molecules. Molecules were discovered much later, and people learned how to measure them in the 1920s. Kepler made the thesis, but it took mankind 300 years to prove it.

Photo by Kenneth G. Libbrecht
Photo by Kenneth G. Libbrecht

How many types of snowflake shapes are there in the world?

That’s an interesting question. There are certain things in the world that you can count, such as tree species. Even though there are still some unknown species, it is generally known where one species of trees ends and another begins. Snowflakes are more like bread. It’s hard to say how many types of bread exist. You can add different types of flour, mix them in different proportions, add some special ingredients. The thing with snowflakes is that you can divide them into a very general type – a shape. But the people who categorize snowflakes have different rules and categories for this distinction. As a result, you can categorize between seven and 120 kinds of snowflake shapes.

Do certain snow shapes only occur in specific geographic locations?

It doesn’t depend on a specific place, but on the temperature. It is a bit too warm in the United States to observe such beautiful snow crystals. The best snowflakes form at around –15˚ C, which again is a bit too cold for Europe.

So which region in the world do you think is the best for snowflake observation?

It depends on what you want to observe. As a snow photographer, I’m always looking for beautiful, star-shaped snowflakes. They only fall between –15 and –10˚ C. It’s hard to spot them in New York, because it’s too warm there. However, when you go a little north, you can see them. But not in Alaska – it’s too cold for star snowflakes there. In Alaska, you can see snowflakes in the shape of a hexagonal prism. For me as a snow photographer, one of the best places to photograph snow is the northern part of Ontario in Canada, where the average temperature in January is around –15˚ C.

Recently, much of Europe has seen a spate of cold, winter weather. What’s the best way to photograph snow?

It’s easy to take good photos, although it’s hard to get really great photos. All you need is a macro lens and then you can take beautiful pictures of snow crystals. At the right temperature, of course. In addition to photography, it is also worth trying to catch and preserve a snowflake.

How can we do this?

It is very easy. The temperature must be to at least –10˚ C. You need two small glass slides – like those used in a microscope – and super glue. Catch a pretty snowflake on this slide. Then put a drop of glue on it so that it covers the entire snowflake. Put a second slide on it. This should all be done outside so that the snowflake doesn’t melt. Leave it outside for around one week. When it’s cold, the glue doesn’t set as quickly as it normally would at room temperature. Once the glue has set, you can bring it inside. The snowflake will be preserved in a drop of glue. You can even make jewellery out of it.

Photo by Kenneth G. Libbrecht
Photo by Kenneth G. Libbrecht

How else can we experiment with snow?

You can make your own ice spikes without leaving your home. Simply pour distilled water into an ice bucket. It freezes into cubes, but ice spikes stick out of those cubes. It’s also worth going outside with a magnifying glass on a snowy day. You can observe beautiful snowflakes. It’s great fun, and nobody does it!

Can I grow my own snowflake at home?

Unfortunately, this is quite difficult. You have to control the temperature and humidity of the air. I do it in the lab.

You also design your own snowflakes in the laboratory. Why?

The idea to design and grow snowflakes with a beautiful star structure came from a practical need. When I became interested in snowflakes, it turned out that there was no book about them. So I decided to write a scientific book about snow crystals. Of course, pictures are part of this book, because who wants to buy a book about snowflakes without any pictures or illustrations of those snowflakes? While working on the graphic design for the book, I found it quite difficult to get good pictures of snowflakes. Since I was already working in the lab, I realized I could make my own snow – which would be better. So I started to do something that I call snowflake design. It’s a slight shift from science to something more artistic. In fact, I design snowflakes in the laboratory more for myself than for science. I can now create better snowflakes in the lab than we can see outside.

Photo by Kenneth G. Libbrecht
Photo by Kenneth G. Libbrecht

What does ‘better snowflakes’ mean? More resistant to melting? More beautiful?

When I photograph natural snow outside, I look for snowflakes that have very sharp and visible edges. They look perfect and symmetrical to me. In nature, however, crystals are often not so symmetrical. On their way to the ground, they melt a little; they hit each other. The sharp edges round off. If you look closely, it is really rare to find such a perfect, undamaged snowflake. And in the lab, I can create complete snowflakes from scratch. That’s why we can define those from the lab as more ideal. It’s like going with your camera into the clouds and photographing snowflakes right after they are formed.

Artificial snow already exists – we can ski down it on a slope. Do you create something similar in the laboratory?

No, artificial snow on the slope is something else. The snow crystals that I create in my laboratory are real snowflakes. They are made of water vapour, not liquid water. It takes about 45 minutes to an hour to grow a nice snow crystal in a laboratory. Just one snowflake! This artificial snow lying on the slopes is made of freezing liquid water. In fact, it is more like ice balls. As long as you only ski on artificial snow, you think it is sufficient. The perspective changes when you discover powder.

Powder is every skier’s dream.

Such beautiful powder is formed precisely from large snowflakes that are born at –15˚ C. It melts a few days after falling.

Is it possible to find two snowflakes that look exactly the same?

Well, have you ever noticed two identical snowflakes?

I’ve never looked at them long enough or carefully enough.

In the United States, many people say that snowflakes are like people – no two are alike. If you are dealing with a very complex snowflake, it is actually very difficult to create an identical one. But on the other hand, there are many hexagonal, crystal-shaped snowflakes that are similar to each other. Besides, what does it mean ‘to be alike’? From a scientific point of view, there are no two things in the world that are exactly alike. There are no two trees or grains of sand that are identical.

Photo by Kenneth G. Libbrecht
Photo by Kenneth G. Libbrecht

Parts of this interview have been edited and condensed for clarity and brevity.

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