The Earth Is a Blue Planet

Seen from space, the Earth appears as a nice blue balloon on which white clouds are often painted. The atmosphere looks like a dome, the color of which varies from the well-known blue to red, according to the time of day. The coloration of the atmosphere is one of the most elegant proofs of electric dipolar radiation.

The atmosphere and clouds work in the same way as a diffuser placed around an electric bulb to ensure a better repartition of the light. Under the action of the electric field of the light coming from the Sun, the electrons of the molecules of the atmosphere are set in vibration and become light sources. By the way, we may notice that the planets that are surrounded by an atmosphere are the only ones to have a clear sky, which is not the case for the Moon.

The diffusion of light occurs differently according to whether it's obtained from independent molecules (mostly nitrogen, oxygen, and water vapor) or from clusters of molecules (water droplets, tiny crystals of ice, dust, aerosols, ). Independent molecules are isolated and separated by distances that are greater than an optical wavelength; since the light of the Sun is not coherent, the different wavelets have random phases and cannot interfere, our eyes will just add their intensities.

Diffusion by droplets or solid particles is different; first, it is more efficient because the number of diffusing particles per unit volume is much...