What is a cloud?

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We can see clouds every day, and there are lots of different kinds of clouds.

In this article you can find out:

  • What a cloud is
  • The process of condensation
  • Different types of clouds and the weather they bring
  • How to measure cloud cover

This resource is suitable for Weather topics for P2, P3, P4, P5, P6 and P7 (First and Second Level Curriculum for Excellence).

What is a cloud?

  1. From a distance, clouds might look like cotton wool but they are actually made from water.

  2. Clouds are formed when the air cools down. This changes an invisible gas in the air called into drops of liquid water, or even tiny ice crystals. This change is called condensation.

  3. The water droplets are big enough to catch the light and allow us to see them, but so small and light that they hang in the sky and don't fall to the ground.

  4. The water droplets all gather together and make clouds.

Different kinds of clouds

Several fluffy clouds float against a blue sky

Clouds come in all shapes and sizes - let's have a look at some of the most common kinds of clouds.

Did you know that there are lots of different kinds of clouds?

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How to measure cloud cover

Clouds play a very important role in what the weather will be like.

With help from BBC Weather's Kawser Quamer, let's find out:

  • Why it is important to measure cloud cover
  • How cloud cover is measured with a lux meter
  • What lux means
  • What the okta scale is

  • cirrus - Thin, wispy clouds that look like feathers and which float around 6000m up in the sky.
  • cumulus - Puffy clouds that look like cotton wool or candy floss. They usually float between 300 and 2000 meters in the sky.
  • stratus - Clouds which often flat and don’t move. On overcast days they stretch across the whole sky like a blanket.
  • nimbus - We add the word ‘nimbus’ to the names of clouds to describe them when there is rain or snow falling from them. For example, a cumulonimbus is a dark puffy thundercloud with rain falling out of it.

Test your knowledge of clouds with this short quiz

Measure cloud cover in the sky today.

There are a number of ways you could do this:

  • Using a meter app on a smartphone or tablet.
  • Using and the .
  • Creating a grid using a mirror tile.

Watch the video above to get more help with measuring cloud cover.


  • Don't look at the sky for longer than a few seconds.
  • Never look directly at the sun.
How to make a cloud cover mirror tile

There's more to learn...