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Our future depends on exploring all the frontiers of science, on innovative technologies based on these explorations and on the development of scientific literacy in all peoples through science education.

Science Around Us – Clouds 1 – Why Are Clouds White

A group of small clouds passing by

Clouds are made up from millions of tiny water droplets that float in the air. The sunlight that shines onto them is a mixture of the rainbow colours which makes the light white. This white light shines onto the droplets and they behave like millions of tiny mirrors reflecting the white light in all directions. The reflection of the light makes the clouds appear white.

Pippa gathered some equipment and materials to make a model cloud.

Pippa in her kitchen lab

She poured some olive oil into the water. In this model the water represents the air and the oil represents the material (the water droplets) in the cloud.

The oil and water ready to be mixed

Pippa stirred up the oil and water. As oil and water do not mix, the oil began to form tiny droplets in the water.

Pippa stirred up the oil and wate

As Pippa stirred the droplets became smaller and smaller until they behaved like the water droplets in a cloud and reflected the white light in the kitchen in all directions.

Pippa’s model cloud

How do clouds stay up in the air?

The billions of water droplets that make up a cloud are smaller in diameter than a hair on your arm. If you could scoop up part of the cloud shown in the first picture and put it in a box measuring one metre square (or about the size of a kitchen fridge) and measure the weight of all the water droplets in it you would find they weighed about as much as one baked bean. This means they weigh very, very little and any upward movement in the air (such as wind or rising air from the warm ground) will keep them in the air.

Next topic – Clouds 2 – How are clouds made?

Science Around Us – Why Is The Sky Blue

Children often ask questions which need a scientific explanation. The memory of the explanations can be extended when an activity is featured. In this series of blogs I have put together some questions that children ask and offered simple explanations which are illustrated by activities that my youngest granddaughter Pippa carried out.

I also include links to other sites to provide further information and details of how to carry out practical work with your children if you wish.

I hope the series will be useful to parents, grandparents and carers for talking about science after school or in the holidays and maybe teachers may find something of interest too.

I am beginning with a series of topics related to the closest thing to us – the air and atmosphere.

Science Around Us 1. Sky colours

Why is the sky blue?

Blue sky above a magnolia tree in Lancashire.

Warning Never look at the Sun in the sky it can damage your eyes!

The colours in the sky come from the rays of light that reach us from the Sun. Sunlight is made up from light of different colours – the colours of the rainbow. Light travels in the form of waves (called electromagnetic waves) and each colour has wave crests that have a certain distance between them. This distance is called the wavelength. Blue light has short wave lengths and red and yellow light have longer wave lengths.

When you look up into the sky you are looking up into the atmosphere. It is made up of molecules of gases, mainly nitrogen and oxygen. As the sunlight shines through the atmosphere the waves of light are scattered and reflected by the molecules of gas. The short waves of the blue light are scattered and reflected the most and this makes the sky blue.

Making a model sky

Pippa has collected items to make a model of the blue sky.

There is an empty olive oil bottle, a torch, a jug of water, a small churn of milk and a teaspoon. The milk will take the part of the molecules of oxygen and nitrogen. Before she uses the milk she makes sure she makes a fair test. This test will show that is the milk the makes the blue light and not the water.

First she fills the bottle with water, places it on its side and shines the torch into the bottle

Shining the torch through water in the bottle.

Next she adds about a third of a teaspoonful of milk to the bottle and shakes it up then shines her torch again.

Shining the torch into the model sky

Why is the sky less blue near the horizon?

A clear sky over the Yorkshire Dales.

In this picture you can see that the sky has become whiter as you look towards the horizon (the place where the Earth meets the sky).
This change is due to the Sun sinking lower in the sky (It is on the left of this picture) and as it does so its light rays pass through a thicker layer of the air. See the picture here.

As the light passes through more air it is more greatly scattered and the different colours of light mix up to make a whitish light.

What makes a sky red?

Red skies can occur in the direction of the Sun at sunrise and sunset. Again it is partially due to the extra thickness of the air that the light passes through but is mainly caused by dust particles and even salt crystals blown up from the surface of the sea. They scatter the blue light completely,but red light is scattered less so making the sky appear red.

Sunrise at Robin Hood’s Bay, Yorkshire

Remember the warning – Never look at the Sun it can damage your eyes.

Here is an experiment to show you how to make a model red sunset.

Next Topic – Why are clouds white?

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I can be contacted in the following ways. If you have a picture for the Natural World Photo Gallery or the Science Exhibition Gallery, please send it by email.