Children ask questions – and we have the answers. This time: where does the snow get its colour from, and how do animals realise it’s time to hibernate?

How do animals know when it’s time to hibernate?

When the days start getting shorter and temperatures drop, many animals know that hibernation time is coming. This is because as soon as they receive less sunlight and it starts getting colder, their bodies react to the changes – and adjust to the cold season all by themselves. The animals then produce much smaller amounts of hormones, and use as little energy as possible. Their hearts beat much less often, for example. So with these first indications of winter, the animals’ bodies automatically go into a resting state. And not being able to find as much food in the autumn is also a sign that it will soon be time for hibernating animals to withdraw for the winter.

Why is snow white and not transparent?

Snow is actually just frozen water. But instead of being transparent like water, it’s white. That’s because a blanket of snow consists of billions of snow crystals, which lie on top of, and next to, each other. When sunlight falls on the blanket of snow, each crystal directs the light on to the next one. There’s air between the individual crystals. And this air means that the light is redirected and appears even brighter. The snow crystals reflect – or bounce back – the light. The sunlight, reflected multiple times and broken up by the air, then radiates back to us. And because sunlight itself is white, the blanket of snow in the winter also appears white to us.