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We have derived the radiative-transfer equation for a point source with aspecified intensity and spectrum, originating in the early Universe between theepochs of annihilation and recombination, at redshifts $z_\s =10^8\div 10^4$.The direct radiation of the source is separated from the diffuse radiation itproduces. Optical distances from the source for Thomson scattering andbremsstrahlung absorption at the maximum of the thermal background radiationare calculated as a function of the redshift z.The distances grow sharply withdecreasing z, approaching asymptotic values, the absorption distance increasingmore slowly and reaching their limiting values at lower z. For the adopted zvalues, the optical parameters of the Universe can be described in a flat modelwith dusty material and radiation, and radiative transfer can be treated in agrey approximation.Comment: 14 pages, 2 figure

Sources of radiation in the early Universe: The equation of radiative transfer and optical distances