[en] Simple diffraction arguments can explain blue suns and moons without needing the full complexity of Lorentz-Mie theory. These rare phenomena give striking evidence of the wave nature of light when the size of the scattering particles is close to the wavelength of light, leading to strong diffraction maxima that allow shorter wavelengths to pass in the forward direction and scatter longer wavelengths into the surrounding sky. The result reverses the colours we normally see in the sky caused by scattering from particles small compared to the wavelength. (note)