Even though sunlight is white
the sky on a sunny day looks blue. This is because sunlight
entering the atmosphere bumps into air molecules and dust
particles, which cause different wavelengths of light to
split off in a process called scattering. The sky looks
blue on a clear day because small atmospheric particles
scatter short blue wavelengths more than the long red wavelengths.
However, at sunrise or sunset, and especially when the air
is dusty, the sky looks red. This is because the sun's light
must travel through the atmosphere for a greater distance
when it is near the horizon. The blue light is bent away
from the eye altogether, while largest dust particles scatter
red light to create a beautiful evening sky.
The sky is blue because tiny particles in the atmosphere
(dust, clumps of air molecules, microscopic water droplets)
are better at deflecting shorter wavelength blue light than
they are at deflecting longer wavelength red light. As sunlight
passes through the atmosphere, enough blue light is deflected
(or more technically Rayleigh scattered) by these particles
to give the atmosphere an overall blue glow. The sun itself
is slightly reddened by this process because a fraction
of its blue light is deflected away before it reaches our
eyes. But at sunrise and sunset, sunlight enters our atmosphere
at a shallow angle and travels a long distance before reaching
our eyes. During this long passage, most of the blue light
is deflected away and virtually all that we see coming to
us from the sun is its red and orange wavelengths. The missing
blue light illuminates the skies far to our east during
sunrise and to our west during sunset
Ever wondered why …
• We sometimes get to witness spectacular sunsets?
• Sky becomes red during after dust storms?
• What is responsible for the blueness of the sky?
• Why does Mars appears red?
• What is Rayleigh scattering?
• Why are clouds white?
Click below for the Answers to these questions and more
on this topics
Besides the answers to above mentioned
questions the animation also contains
- Explanation based on atmospheric
refraction and scattering
- Detailed explanation of Rayleigh