Why is the sky blue?

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The question:

Why is the sky blue? Why does it turn red at sunset? Curious mind wants to know.

The answer:

If you have very little knowledge of science, you have to understand some easy facts first.

The facts:

1. Sunlight is a composite ray. This is why we see a rainbow. The white ray of the sun is composed of 7 visible colors (violet, indigo, blue, green, yellow, orange, and red) along with other rays (x-ray, infrared ray, etc.). You can test it yourself with a prism.

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2. Light spreads like a wave. So, sunlight is a wave that is composed of different waves or rays. Different waves are of different wavelengths. The shorter the wavelength of a wave is, the more it is scattered by particles (gas, dust, etc.). And the longer the wavelength of a wave is, the less it is scattered by particles. Thus, a wave with a shorter wavelength can pass a longer distance.

3. Blue light waves are shorter than red light waves.

4. Human-eyes are more sensitive to blue light than other short wave lights.

Why is the sky blue then?

While penetrating the earth's atmosphere, sunlight is scattered in all directions by all the gases, dust, and other particles in the air. Among all the colors, blue light is scattered the most because of its shorter, smaller wavelength. This is why the sky looks blue in the day time.

Why is the sky not violet or indigo?

Violet has the shortest wavelength of all 7 colors, but it is less sensitive to human-eyes than blue. Violet and Indigo colors are also absorbed in a large quantity by the high atmosphere.

Why does it turn red at sunset?

As the sun goes down near the horizon, its light has to pass more distance in the atmosphere to reach your eyes. Here wins the red light. Because blue is more scattered because of its short wavelength. This is why we see the sky red in the sunset.

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