Published the 20 December 2014
Then a very innocent question comes out of nowhere: Why is a snowflake shaped like a star? Oops...do you have any idea what to reply? The answer is here !
What is snow? It’s many different snowflakes!
To make snowflakes you need water, cold temperatures and a few impurities.
When temperatures go below 0°, an ice crystal forms around an ice nucleus (impurities hanging in the atmosphere) in a cloud. This nucleus feeds on the water surrounding it.
The crystal «absorbs» the hanging water droplets, «transforming» them into crystals too. All of these crystals then «stick» together.
Subsequently, the snowflake will get heavier, increasing in size, and the weight of it will make it fall (very slowly to start with, then faster and faster). However, if a snowflake crosses a mass of air which is warmer than 0 degrees, it will melt… turning into a rain drop.
As it falls, the snowflake will carry on picking up other elements: this is known as coalescence. In a thick dense cloud (such as a nimbostratus and most cumulus clouds), the internal amalgamation increases the chances of a collision with others, in turn making larger snowflakes.
But why does a snowflake always have 6 branches?
Because the smallest shape of an ice crystal is a hexagon, so when the crystals stick together, 6 branches create around the ice nucleus.
But even if a snowflake always has 6 branches, no two snowflakes are ever the same. Dampness, the temperature and bumps with other snowflakes will all have an impact on it… the shape of a snowflake is part of its make-up.
An American farmer, Wilson Bentley, spent 40 winters taking photographs of snowflakes. In the thousands of images taken, he never had two identical ones!
Even if we can’t predict the shape of a snowflake, we can make a few observations > the colder it is, the longer its six branches will be > in warmer temperatures, the branches will widen without growing longer.
At temperatures close to 0°C, snowflakes are damp and cluster together easily, sometimes making large snowflake clusters. However, crystals that move through very cold air are hard and don’t cluster well with others. Many land on the ground on their own, if the cold conditions continue as they fall.