What are clouds made of?

How it works

The Sun warms oceans, lakes and land, and some water evaporates into water vapour, which rises with warm air. Higher up, the air is colder. When the vapour cools enough, it condenses, meaning it turns back into liquid, around tiny specks of dust or sea salt, forming droplets.

These droplets are far smaller than even a grain of fine sand, so they fall incredibly slowly, and rising air keeps holding them up. Billions upon billions of them together scatter sunlight in every direction, which is why most clouds look white.

When a cloud is very thick, little sunlight gets through, so its base looks grey, often a sign of rain. High, wispy clouds called cirrus are made almost entirely of ice crystals. When droplets bump together and grow too heavy to stay up, they fall as rain.

Where to see it in New Zealand

New Zealand's Māori name, Aotearoa, is often translated as 'land of the long white cloud'. In Canterbury, when north-west winds blow over the Southern Alps, a long band of cloud called the nor'west arch often stretches across the sky.

Try it together

On a cold morning, breathe out and watch the white puff appear, or breathe on a cool mirror. The water vapour in your breath was invisible until it cooled into tiny droplets. You have just made a mini cloud.