Why is the sky blue?

Okay, we started off with an easy question, let's move on to a traditional one!

This is probably one of the toughest (and most frequent) questions parents are asked, though the answer is actually quite simple. The visible light we have here on Earth comes from the Sun. Sunlight looks white, but is actually a mixture of all of the c olors of the rainbow. When sunlight strikes very small objects like air molecules and dust particles, the light itself is deflected in all directions, forward, sideways, and backwards. This is called Raylei gh scattering.

Because air molecules are much smaller than the wavelengths of visible light, they are more effective scatterers of the shorter (blue) wavelengths than the longer (red) wavelengths. In fact, blue light is scattered at least 10 times more than red light. Thus, the blue rays of lights are scattered the most and reach our eyes from all directions so we see more blue than any other color, and this makes the sky look blue.

Earth, by the way, is not the only planet with a colorful sky. On Mars, dust in the air turns the sky red at midday and purple at sunset.

Submitted by Carlos (Texas, USA)
(July 28,1997)

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