Sky is BLUE

The sky is blue because of the phenomenon called the ‘Tyndall effect’. This is the scattering of light, as it passes through particles in suspension. Due to its short wavelength, the elements in the atmosphere happen to scatter blue more than any other colors.

When the sun is shining down on the Earth, most of the other wavelengths or colors travel in a relatively straight line. The Sun appears white because it contains almost all the visible colors. The rest of the sky appears blue because we are seeing the blue light that has been scattered by the atmosphere.

Sunsets and the Sun during dusk appear as red and orange because there are more atmospheres for the light to travel through and more blue is deflected. Red is one of the longer wavelengths, so it is scattered the least, thereby making the Sun and sky appear redder.


The white light from the Sun is a mixture of all colors of the rainbow (i.e. VIBGYOR). This was demonstrated by Isaac Newton, who used a prism to separate the different colors and so form a spectrum. The colors of light are distinguished by their different wavelengths. The visible range of the spectrum varies from red light with a wavelength of about 720 nm, to violet with a wavelength of about 380 nm, with orange, yellow, green, blue and indigo between them. The three different types of color receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our color vision.

The first steps towards correctly explaining the color of the sky were taken by John Tyndall in 1859. He discovered that when light passes through a clear fluid holding small particles in suspension, the shorter blue wavelengths are scattered more strongly than the red. This can be demonstrated by shining a beam of white light through a tank of water with a little milk or soap mixed in it. From the side, the beam can be seen by the blue light it scatters; but the light seen directly from the end is reddened after it has passed through the tank. The scattered light can also be shown to be polarized using a filter of polarized light, just as the sky appears a deeper blue through Polaroid Sun glasses. This phenomenon is called the ‘Tyndall effect’, but it is more commonly known to physicists as ‘Rayleigh Scattering’, after Lord Rayleigh, who studied it in more detail a few years later. He showed that the amount of light scattered is inversely proportional to the fourth power of wavelength for sufficiently small particles.