[Science World]Blue skies, poets, politicians

The sky looks blue because of the reflection of light in the atmosphere. Rays of light of various wavelengths arrive at the Earth, but rays of blue light, which has the shortest wavelength, are reflected more sharply than other light and are dispersed widely when they hit the atmosphere. The scattered blue rays enter our eyes and this is why the sky appears to be blue.

Although we always see the blue sky on a clear day, that does not mean that the sky is unchangeably blue in its characteristics. The color of the sky changes in different circumstances. On a clear day, the sky looks blue, but the sky appears to be yellow, especially when yellow dust fills the air as has happened in recent days. At twilight, the sky turns to red, and without light at night, the sky is dark. On the moon, where there is no atmosphere, the sky always looks dark, regardless of whether it is day or night, because there is no dispersion of light in the absence of an atmosphere.

What is more important is that the color of the sky changes depending on the person who is looking at it. People with normal vision have seen the blue sky innumerable times since their birth, and thus they always believe that the sky is blue. But this is not true. The sky does not appear to be blue through the eyes of animals that cannot distinguish the color blue. For example, the sky may appear to be yellow for animals that can only sense yellow and to be purple for animals that can only sense purple light.

Light that human beings recognize represents only a small part of the entire electromagnetic spectrum. The visible light region is the only range of energy that human eyes can detect. From the low-energy end (at about 7000 Angstroms) to the high-energy end (at about 4000 Angstroms), the visible spectrum conveys the world to our brains in brilliant hues and shades. Within the visible light region is the rainbow of colors starting from red and proceeding to violet. Because of our range of vision, we see a blue sky.

In other words, the color of the sky is blue not because the sky itself is blue, but because of our human-centered interpretation of the world. We generalize from a special circumstance - the earth on a clear day - and conclude that what we see is a universal phenomenon.

The sky is blue because of the relationships that exist in our world, especially the existence of the atmosphere and our ability to sense the color blue. Organisms that have existed on the earth largely created the atmosphere, and our vision is a product of evolution that has been going on for 3.5 billion years. Thus, the act of looking at the blue sky, though simple, is a result of the whole history of living things on earth.

Politicians complete their speeches on their own, but poets do not complete their poetry only by writing it; poetry is completed when it enters the minds of readers. The world in which the blue sky is conjured up by our vision is closer to a poem than to a politician's speech.

The writer is a professor of physics at Korea University.

by Yang Hyung-jin