Among all of the perennial questions children ask about this planet, the most common would be “why is the sky blue?” Either we have asked this question at some point in our childhood or we have children asking us this question now.
The answer of this question lies within the ultimate source of light on our planet which is sun. This light appears to be white but it actually contains all the colors of a spectrum from red color to violet.
Color bands and the spectrum
When the sunlight travels through the atmosphere to reach earth it is reflected, altered and absorbed through many objects and surfaces. It passes through many objects, particles and compounds.
The color sky seems to a naked eye is mainly dependent on the wavelengths of the incoming light. Other entities which play a role are air molecules (mainly oxygen and nitrogen). Moreover, dust particles also play an important role.
When the sun is right above our heads, the rays reach earth at nearly vertical/straight angle. Shorter wavelength of light e.g. violet and blue get absorbed in the air molecules easily as compared to the longer wavelength of light i.e. yellow, orange, red etc.
Then the air molecules start radiating violet and blue light in all directions which saturates the entire sky. However, we see blue color in the sky because our eyes are more sensitive to blue color than to violet.
Passage of light
When the sun is about to rise or set during the dusk or dawn, the rays of light fall on to the earth in a slanted angle. These rays have to travel a much greater distance to reach earth compared to what they travel during the midday.
This is where a lot of oxygen, nitrogen and other particles try to block the sunlight. As a result the sunlight is scattered. During this passage of light enroute earth the blue and violet light is mostly filtered out. The effect of these shorter wavelengths diminishes.
However, the longer wavelengths strike the dust and other particles near the horizon. These rays also fall on the water droplets which make clouds in the sky. This is how we see the orange, red and yellow color during the beautiful sunsets.