Final answer:
Albert Einstein explained why the sky is blue, attributable to Rayleigh scattering, in his work on the scattering of light, not in a paper specifically on opalescence.
Step-by-step explanation:
The physicist who explained why the sky is blue in a 1910 paper on opalescence was Albert Einstein. This phenomenon is explained by Rayleigh scattering, where molecules and small particles in the Earth's atmosphere scatter sunlight in all directions, and blue light is scattered more than other colors because it travels as shorter, smaller waves. Although Niels Bohr made significant contributions to the understanding of atomic structure and quantum mechanics, describing the atomic spectrum of hydrogen using Rutherford's planetary model of the atom, it was Einstein who tackled the question of the sky's color, not in a paper specifically on opalescence but in his broad work on the scattering of light.