The haze which appears to surround any distant object is due to an optical phenomenon called 'Rayleigh scattering'. This effect causes the rays of light which impinge on small particles to be scattered in various directions. The blue haze, unique to the Blue Mountains, is of a different hue and deeper than anywhere in the world. It is cause primarily by Eucalyptus trees emitting oil vapour into the atmosphere which along with fine dust particles and droplets of water vapour, scatter blue light (blue light is short wave-length) more than any other spectrum colour.
