Elliot - WHY IS THE SKY BLUE AND THE SUN YELLOW?

I did an experiment at home to show how blue light scatters.

First I filled a transparent container with warm water.  Then I shone a torch through the container on to a white piece of paper.  The light on the paper looked white with a bit of blue around the edges.

Shining a Torch Through Clear Water

From the side the water was clear.

Side View

I then added some milk powder to make the water a bit cloudy so that the beam of light from the torch could be seen in the water.

Adding Some Milk Powder

It wasn't enough so I added even more.

Adding Even More Milk Powder

And then I stirred the milk powder so that it would dissolve in the water.  The water immediately appeared blue.

Stirring In the Powder

The light on the white paper appeared yellowish.

The Light on the White Paper

From the side you can see the contrast of the bluey water and the yellow spot on the white paper.

A Side View of the Milky Water and the White Paper

Explanation

When white light comes toward us through the earth’s atmosphere from the sun, it bumps into different gas molecules like oxygen and nitrogen and some of it gets absorbed.  Shorter-wavelength-light, like violet and blue, are absorbed more than longer-wavelength-light.  So the red, orange and yellow light pass straight through the atmosphere.  However, the absorbed violet and blue light are then radiated and get scattered all around the sky.  The sun puts out much more blue light than violet so the sky looks blue.  This is known as Rayleigh scattering, the English scientist who first described this.

Lord Rayleigh (1842-1919)

The sun appears yellow because when the shorter-wavelength-light, the blues and violets, are scattered from the direct rays of the sun the remaining colours together appear yellow.