Discovery Posting Ninety:
Have you ever wondered why the sky is blue?
To answer this question, we need to explore about a little about earth's atmosphere and light.
According to Wikipedia, Earth's atmosphere (or air) is a layer of gases surrounding the planet Earth that is retained by the Earth's gravity. Dry air contains roughly (by volume) 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and trace amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%.
Other particles such as dust, soot and ashes, pollen and salt from the oceans can also be found in the atmosphere.
Light is made up of many colours. These colours include red, orange, yellow, green, blue, indigo and violet. At the same time, light is a kind of energy that travels in waves, just like sound. The colours that make up light possess different energy levels.
Violet, for example, possesses the highest energy and also, take note, the shortest wavelength. For the colour of red, it possesses the lowest energy and the longest wavelenght.
Why is the sky blue?
As light moves through the earth's atmosphere, most of the colours which have longer wavelengths pass straight through. Thus, little of the red, orange and yellow light is affected by the air.
However, colours with shorter wavelength is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. They then get scattered all around the sky. So whichever direction you look, some of this scattered blue light reaches you. And since you see the blue light from everywhere overhead, the sky looks blue.
For a more detailed reading on this topic, please refer to http://www.sciencemadesimple.com/sky_blue.html.