
English: 
Hey! Radical Thought.
Today’s Radical Question is: Why is the
sky blue? Why isn’t it violet?
White light as we know it is actually a mixture
of 7 different colors that we can see. If
you ever place a prism in a beam of sunlight
you will find it separates into different
colors. The spectral colors of white light
all have different wavelengths.
Light usually travels in a straight line unless
it witnesses an obstacle and observes one
of three particular phenomena. These phenomena
are ‘Reflection’, ‘Refraction’ or
‘Rayleigh Scattering’.
Reflection is a phenomenon in which light
simply bounces of a surface at the same angle
it hits, just like a mirror.
In refraction light bends at a particular

English: 
Hey!
Radical Thought.
Today’s Radical Question is: Why is the
sky blue?
Why isn’t it violet?
White light as we know it is actually a mixture
of 7 different colors that we can see.
If you ever place a prism in a beam of sunlight
you will find it separates into different
colors.
The spectral colors of white light all have
different wavelengths.
Light usually travels in a straight line unless
it witnesses an obstacle and observes one
of three particular phenomena.
These phenomena are ‘Reflection’, ‘Refraction’
or ‘Rayleigh Scattering’.
Reflection is a phenomenon in which light
simply bounces of a surface at the same angle
it hits, just like a mirror.
In refraction light bends at a particular
angle once it changes its medium of travel;

English: 
angle once it changes its medium of travel;
just like a prism.
The third phenomenon is related to why the
sky is blue.
See, the earth’s atmosphere is comprised
of tiny particles of numerous gases including
nitrogen and oxygen. When sunlight shines
on these particles it bounces off in different
directions. This phenomenon is called Rayleigh’s
Scattering.
According to Rayleigh the scattering intensity
is inversely proportional to the wavelength
of the fourth power. This means that shorter
wavelengths like violet will scatter 9 times
more than longer wavelengths like red.
But then why doesn’t the sky appear violet
or indigo? since their wavelengths are smaller
than blue. There are two reasons for that.
One being that sunlight has more blue light
in it than violet. Secondly the cone cells

English: 
just like a prism.
The third phenomenon is related to why the
sky is blue.
See, the earth’s atmosphere is comprised
of tiny particles of numerous gases including
nitrogen and oxygen.
When sunlight shines on these particles it
bounces off in different directions.
This phenomenon is called Rayleigh’s Scattering.
According to Rayleigh the scattering intensity
is inversely proportional to the wavelength
of the fourth power.
This means that shorter wavelengths like violet
will scatter 9 times more than longer wavelengths
like red.
But then why doesn’t the sky appear violet
or indigo? since their wavelengths are smaller
than blue.
There are two reasons for that.
One being that sunlight has more blue light
in it than violet.

English: 
in the human eyes are well tuned to detect
three colors red, blue and green. As human
beings we recognize blue easily compared to
violet. And that’s why the sky appears light
blue to our eyes.
This is truly a blessing; due to this, our
atmosphere seems illuminated in the daytime.
If this phenomenon did not occur or if our
atmosphere was absent; we would only see sunlight
from one direction with black sky; which will
not be much use; as it would be similar to
using a flashlight in a dark room.
Now let’s say for sake of argument that
our Sun’s light spectrum starts to shift,
and it now has more violet than blue. Imagine
what it would be like if our sky was purple.

English: 
Secondly the cone cells in the human eyes
are well tuned to detect three colors red,
blue and green.
As human beings we recognize blue easily compared
to violet.
And that’s why the sky appears light blue
to our eyes.
This is truly a blessing; due to this, our
atmosphere seems illuminated in the daytime.
If this phenomenon did not occur or if our
atmosphere was absent; we would only see sunlight
from one direction with black sky; which will
not be much use; as it would be similar to
using a flashlight in a dark room.
Now let’s say for sake of argument that
our Sun’s light spectrum starts to shift,
and it now has more violet than blue.
Imagine what it would be like if our sky was
purple.

English: 
Would we enjoy the new change? or dread the
toxic looking color?
After all it’s highly likely that there
are other planets with different colored skies.
So what do you think?
Leave a comment.
And as always, thanks for watching.

English: 
Would we enjoy the new change? or dread the
toxic looking color? After all it’s highly
likely that there are other planets with different
colored skies. So what do you think? Leave
a comment.
And as always, thanks for watching.
