Map of Egypt

Map of Egypt.

Map of Ecuador

Map of Ecuador.

Why is the sky blue?

To understand why the sky is blue, we first need to understand a little bit about light. Although light from the sun looks white it is really made up of a spectrum of many different colours, as we can see when they are spread out in a rainbow.

We can think of light as being a wave of energy, and different colours all have a different wavelength. At one end of the spectrum is red light which has the longest wavelength and at the other is blue and violet lights which have a much shorter wavelength.



Why is the sky blue?
When the sun's light reaches the Earth's atmosphere it is scattered, or deflected, by the tiny molecules of gas (mostly nitrogen and oxygen) in the air. Because these molecules are much smaller than the wavelength of visible light, the amount of scattering depends on the wavelength. This effect is called Rayleigh scattering, named after Lord Rayleigh who first discovered it.

Shorter wavelengths (violet and blue) are scattered the most strongly, so more of the blue light is scattered towards our eyes than the other colours. You might wonder why the sky doesn't actually look purple, since violet light is scattered even more strongly than blue. This is because there isn't as much violet in sunlight to start with, and our eyes are much more sensitive to blue.

The blue light that gives the sky its colour, is sufficiently bright to make all the stars that we see at night disappear since the light they emit is much dimmer.


Why does the blue fade towards the horizon?

You might also notice that the sky tends to be most vibrant overhead and fades to pale as its reaches the horizon.This is because the light from the horizon has had further to travel through the air and so has been scattered and rescattered. The Earth's surface also plays a role scattering and reflecting this light.

As a result of this increased amount of scattering, the dominance of blue light is decreased and so we see an increased amount of white light.

Map of East Timor

Map of East Timor.

Map of Dominican Republic

Map of Dominican Republic.

Map of Dominica

Map of Dominica.

Map of Djibouti

Map of Djibouti

Map of Denmark

Map of Denmark.

Map of Democratic Republic of Congo

Map of Democratic Republic of Congo.

Map of Czech Republic

Map of Czech Republic.

Map of Cyprus

Map of Cyprus.

Map of Cuba

Map of Cuba.

Map of Croatia

Map of Croatia.

Map of Cote d'Ivoire

Map of Cote d'Ivoire.

Map of Costa Rica

Map of Costa Rica.

Map of Comoros

Map of Comoros.

Map of Colombia

Map of Colombia

Map of China

Map of China

Map of Chile

Map of Chile

Map of Chad

Map of Chad

Map of Central African Republic

Map of Central African Republic

Map of Canada

Map of Canada

Map of Cameroon

Map of Cameroon.

Map of Cape Verde

Map of Cape Verde

Map of Cambodia

Map of Cambodia

Map of Burundi

Map of Burundi

Map of Burkina Faso

Map of Burkina Faso.

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