The Science of Snowflakes Why No Two Are The Same

What is a snowflake

A snowflake is a small piece of ice that falls from a cloud as snow. Each snowflake starts when water in the air freezes around a tiny speck such as dust or pollen. As more water vapour in the cloud freezes onto this little crystal it begins to grow into a snowflake.

Snowflakes are made of clear ice but they look white because light bounces and scatters off many tiny crystal surfaces. When millions of flakes fall together they create the soft white blanket that children love to play in.

Why do snowflakes have six sides

To understand snowflakes we need to think about water. Every water molecule has one oxygen atom and two hydrogen atoms. When water freezes into ice these molecules lock together in a repeating pattern that has a hexagon shape. A hexagon has six corners.

Because of this pattern deep inside the crystal every snowflake grows with six sides or six main arms. Even though the shapes we see are very different the number six appears again and again in the design.

How a snowflake grows inside a cloud

High up in a cold cloud the air is full of tiny droplets and invisible water vapour. When the air is cold enough a droplet can freeze onto a dust speck and become the start of a snowflake. From that moment the snow crystal begins a long journey through the cloud.

As the young snowflake drifts it passes through parts of the cloud that have different temperatures and different amounts of water vapour. In some places the air is very moist so the arms of the snowflake grow quickly and form delicate branches. In drier parts of the cloud the growth slows and the shape becomes simpler.

Sometimes the crystal grows as a thin flat plate. At other times it grows as a long needle or a more solid shape. All of these changes depend on the conditions in the cloud air that the snowflake passes through.

Why no two snowflakes are exactly the same

Now imagine how many tiny decisions happen as a snowflake grows. Every moment the air around it may change slightly. It might become a little colder or a little warmer. There may be a little more or a little less water vapour. Each change affects the way new ice forms on the arms of the snowflake.

No two snowflakes follow exactly the same path through a cloud. That means they never share exactly the same history of temperature and moisture. Even if two flakes start in nearly the same place, tiny differences in their journey will change how their branches grow. Over time these small changes add up and the pattern becomes unique.

Scientists have photographed thousands of snowflakes and found that the chance of two large natural flakes being perfectly identical is extremely small. There are simply too many ways for the pattern to grow and too many different conditions inside real clouds.

Can snowflakes ever look alike

Very simple snow crystals that form quickly and do not grow many branches can sometimes look almost the same. In special laboratory experiments scientists have even grown matching snowflakes by carefully controlling the air and temperature around them.

Out in nature however the air in clouds is always changing. That is why the saying no two snowflakes are alike is still a good way to explain how special each one is, especially when we are talking about the larger and more detailed flakes that children can see on their coats or mittens.

Snowflakes as tiny weather records

Because snowflakes are so sensitive to their surroundings, their shapes give clues about the weather inside the clouds where they formed. For example, very feathery snowflakes usually grow in air that is quite moist, while simpler shapes may grow in drier air. In this way each snowflake is like a tiny frozen record of the cloud it came from.

Snowflake science activities for children

There are many simple ways to turn snowflake science into hands on fun.

• On a snowy day, invite children to catch snowflakes on a dark sleeve or piece of card and look closely at the shapes before they melt.
• Ask children to count the arms on different flakes that they can see.
• Create paper snowflakes by folding and cutting white paper, then compare how each one is different.
• Use a magnifying glass to explore ice crystals in frost on cold mornings.

These activities show that science is all around us and help children link what they see in the real world with ideas about molecules, patterns and temperature.

Bringing it all together

Snowflakes are not just pretty winter decorations. They are tiny crystals that follow the rules of chemistry and physics as they grow. Water molecules arrange themselves into a six sided pattern, clouds provide the cold air and moisture, and the ever changing journey of each flake shapes its final design.

When children learn that every snowflake has its own story they also learn to see the natural world in a new way. The next time snow begins to fall you can step outside together, look closely at the flakes and enjoy a winter science lesson that is cool, creative and full of wonder.