Why is the sky blue?

Prism defracting the-visible-spectrumThe light from the Sun looks white. But it is really made up of all the colours of the rainbow. 

When white light shines through a prism, the light is separated into all its colours. A prism is a specially shaped crystal.  The light you see is just one tiny bit of all the kinds of energy beaming around the universe and around you! We call it the visible spectrum because the human eyes and brain can translate all this energy into the colours of our beautiful planet.   

Like energy passing through the ocean, light energy travels in waves, too. Some light travels in short, “choppy” waves. Other light travels in long, lazy waves. Blue light waves are shorter than red light waves.

All light travels in a straight line unless something gets in the way and does one of these things:—

  • reflect it back (like a mirror)
  • bend it (like a prism)
  • or scatter it when it bumps into other particles (like molecules of the gases in the atmosphere)

Sunlight reaches Earth’s atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth’s atmosphere. 

Because Blue light is scattered much more than other colours as it travels as shorter, smaller waves, we can ‘see’ these blue waves more clearly.  

As we look towards the horizon, the blue colour tends to fade, often to white. This is because between our eyes and the horizon, all the different wavelengths of light are scattering so much that the colourful components of the visible spectrum appear to recombine to form WHITE LIGHT..  

As many sky watchers, artists and photographers will be aware, we see many colours within most skies, especially when clouds are around! 

These colours depend on what types of particles are present in the air for the light rays to bounce off. We will all be familiar with the colours created by dust or sand in the atmosphere. 

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