The document explains why the sky appears blue. It discusses how light scatters in the atmosphere, with shorter blue wavelengths of light scattering more than longer red wavelengths. This causes the sky to appear blue, as the scattered blue light from the sun reaches our eyes from more angles. Variations in sky color at different times of day are due to changing amounts and sizes of particles in the atmosphere that cause more or less light scattering. The document explores this phenomenon through discussing the nature of light as waves and how prisms can separate white light into visible colors.