It is right above our head and we see that day in and day out. In fact this what determines our day.
But never really wondered what is the reason behind this.
Here goes the reason.
As we all know light from sun is made of the VIBGYOR colors.
With Violet having the shortest wavelength and highest frequency
And Red with longest wavelength and shortest frequency.
Sunlight when it passes through earth's atmosphere collides with the air molecules.
These molecules scatter the light. Shorter wavelength scattered easily than longer ones.
So Violet, Indigo and Blue are scattered the most.
Resonance Effect - Chain Reaction
Blue light also has a frequency that is closer to the resonant frequency of atoms than that of red light.
That is, if the electrons bound to air molecules are pushed, they will oscillate with a natural frequency that is even higher than the frequency of blue light.
Blue light pushes on the electrons with a frequency that is closer to their natural resonant frequency than that of red light. This causes the blue light to be reradiated out in all directions, in a process called scattering.
The red light that is not scattered continues on in its original direction. When you look up in the sky, the scattered blue light is the light that you see.
Why blue and not violet?
Violet light has an even shorter wavelength than blue light: It scatters even more than blue light does.
So why isn't the sky violet?
Because there is just not enough of it. The sun puts out much more blue light than violet light, so most of the scattered light in the sky is blue.
Why does the Sunset look reddish?
When the sun is on the far end of the horizon, its light takes a longer path through the atmosphere to your eyes than when the sun is directly overhead. By the time the light of the setting sun reaches your eyes, most of the blue light has been scattered out. In the previous case the blue light didn't have to travel long so it had the right amount of scattering to fill in the place. This time around it is longer distance, more molecules and it loses its steam and gets dispersed away.
The light you finally see is reddish orange, the color of white light minus blue.
A Simpler Try :
Now All this is scientific. So i just tried to make it a little easier with a little example so that this can be explained to kids.
Imagine a circular target like in a dart board.
And consider a transparent paper filter or screen placed in front it.
Imagine 7 individuals each having a particular type of Arrow and bow. They are aiming at the center of the target.
Consider the first arrow to be made of light material like a stem of a plant carrying a very tiny match stick in front of it.
Consider third arrow to be made of wood carrying a large flame of fire.
Consider the last arrow to be made of a heated iron material.
Now the first arrow might not even reach the screen even if it reaches it is not going to light up the screen.
Map this to Violet.
Second arrow would reach the screen and is going to light up the entire paper screen.
Map this to blue.
Third arrow would easily pierce the screen and keep going inside. Wouldn't exactly light up the screen as it keeps going.
Map this to Red.
Map the circular target for Earth.
Map the paper screen to the earth's atmosphere [with air molecules].
Seven arrows to be the VIBGYOR.
Now when does the paper screen [earth's atmosphere] get lit up [appears blue]?
When the third arrow [B in VIBGYOR] lights up the paper [atmosphere] and spreads through out.
