Brightness and Color of Astronomical Objects

The atmosphere of the Earth absorbs virtually all of the grays, x-rays, and most of the ultraviolet and infrared radiation, and the ionosphere reflects and scatters away much of the radio frequencies from space. Even in the absence of cloud, however, the atmosphere is an absorbing and scattering medium for visible light. Atmospheric molecules scatter blue light much more strongly than red light, resulting in a yellow or reddish sunset and a blue sky. This type of scattering is called "Rayleigh scattering," after Lord Rayleigh (the title of John William Strutt, 1842-1919), who first explained the phenomenon in 1871. The scattering is inversely proportional to the fourth power of the wavelength (i.e., we may write, o « 1/14). The moon and other




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