ASK! about Science & Technology 

Before you jump into this, do you know what is colour?

Colour is the complement of the wavelengths of light that reaches our eye. If a cube appears red, that’s because it is reflecting red light into our eyes.

Now sunlight contains the whole visible spectrum of light, from violet to red. The colour of the sky we see depends on the wavelength of light that reaches our eyes. When sunlight travels throught the sky, it is scattered by the air molecules. This effect is explained by Rayleigh scattering. The lower the wavelength of light, or the greater the amount of particles passed it will pass through, the higher the scattering effect.

On a clear day, blue light (lower wavelength) will be scattered more than red light. Hence, the background of the sky appears blue. The yellow, orange and red light are scattered less and appear to come directly form the sun. Thus, the sun looks bright yellow.

At dusk or dawn, the sun is low on the horizon. Sunlight is scattered more as it travels through a greater amount of atmosphere. The background of the sky appears dark blue, while the clouds are tinted pink or orange as yellow and red light are scattered less and travel straight into our eyes.

Questions like this are called imponderables. Perhaps because they are so puzzling and popular, books have been written to answer them. Find out here.

Reference:
1. New Scientist, 2006, Why don’t penguins’ feet freeze?, London, Profile Books: pg 153-155. (Call No.: 500 WHY)
2. Hart-Davis, A. 2005, Why does a ball bounce? and 100 other questions from the world of science, London, Ebury Press: pg 89. (Call No.: 500 HAR)
3. Kusky, Timothy. “why seawater is blue.” Encyclopedia of Earth Science. New York: Facts On File, Inc., 2005. Science Online. Facts On File, Inc. http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin= EOES0614&SingleRecord=True (accessed June 23, 2008).

Posted by Ang Mei Jun,

Librarian, Adult & Young People’s Services

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