Why the Sky is Blue
The scattering that produces the blue sky is called Rayleigh scattering. Tyndall (1859) and Rayleigh (1870s) first explained the effect.
Tyndall and Rayleigh thought the scattering was caused by small particles of dust and droplets of water vapour in the atmosphere. Others realised that if this were the case, sky colour would vary more with humidity and haze. They conjectured that the oxygen and nitrogen molecules in the air caused the scattering.
Einstein (1911) finally settled the matter. He calculated the detailed formula for the scattering of light by molecules. His calculation agreed with experiments. It independently verified the experimental determination of Avogadro's number.
Through the work of many scientists, culminating in that of Einstein, we learned that gas molecules scatter light because the electromagnetic field of light waves induces electric dipole moments in molecules.
