Wednesday, January 2, 2013

Why Is the Sky Blue?

The Color of the Sky

The nineteenth-century British scientist John Tyndall explained the color of the sky by using the image of the sea.

“Think of an ocean and think of the waves crashing against the land. If they came across a huge cliff then all the waves would stop; if they met a rock then only the smaller waves would be affected; while a pebble would change the course of only the tiniest waves washing against the beach. This is what happens with light from the sun.

Going through the  atmosphere the biggest wavelengths—the red ones—are usually unaffected, and it is only the smallest ones--the blue and violet ones—which are scattered by the tiny pebble-like molecules in the sky, giving the human eye the sensation of blue.”

Tyndall thought it was particles of dust which did it; Einstein later proved that even molecules of oxygen and hydrogen are big enough to scatter the blue rays and leave the rest alone.  But the effect of both theories is the same. At sunset, when the air is polluted with molecules of dust—or, over the sea, little salt particles—both of which act as ‘rocks’ rather than ‘pebbles’ in disturbing the wavelengths of light, the sky will seem orange or even red.”


Victoria Finlay wrote of this phenomenon in her book Color: A Natural History of the Palette. She tracked down the source of most colors in amazing trips around the globe which are highlighted in this fascinating account of her pursuits.

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