[Music]
>> (child) Hey dad, the sun becomes red when
it goes down.
And why is the sky blue?
>> (dad) Little girl : when the sun is high
in the sky, it is white with yellow shades.
The sun gives light, itself made up of different
colours.
You can see it in the rainbow when the light
is split because of the rain.
When all those colours arrive at the same
time in our eyes, our brain perceives it as
white.
Around the earth, you have the atmosphere
who's permit us to breathe.
This is amongst other things made up of 1/5th
of oxygen.
Don't tell it to anyone else but the blue
light is in love with oxygen.
They don't feel blue...
The green light is also in love but less.
She isn't as green as grass.
When the red, orange or yellow part of the
sunlight meets oxygen, it spreads a little
bit.
On the other hand, when blue light meets oxygen,
it throws sparks !
All those meetings between blue light en the
molecules of oxygen makes that the sky becomes
blue.
During a sundown, the way of the light who
goes through the atmosphere is more long.
The molecules of oxygen at the start of the
way absorb all the blue light.
Only the range of red light remains.
That's why you can see the sun with this colour.
It's thus not because it is shy and wants
to hide...
This rule of diffusion of the light, that
we call diffusion of Rayleigh, is only valid
for little particles like oxygen molecules.
That rule is thus not true for tiny water
drops which compose the clouds.
All the colours are diffused on the same way
and it's therefore that the clouds are white.
Some clouds are grey because they are more
thick and light has difficulties to go through
it.
This phenomenon also explains why, during
a total eclipse of the moon, the moon is reddish
even when she should be hidden by the shadow
of the earth.
Brilliant, no ?
Do you understand now ?
>> (child) Actually... not at all...
