I have been googling Cosmic Background Radiation, but am still confused as to the location of its source. Is it just very old light finally arriving from very distant sources? Or is earth also surrounded by nearby CBR sources that in the fullness of time will arrive at very distant galaxies?
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The source is all the matter in the universe. When matter formed after the big bang it was still very hot and was plasma, which is an ionized gas. Plasma is not transparent to light so the light the warm material emitted got absorbed again.
The matter was called down when the universe expand and approximately 379,000 years after the big bang was cold enough and no longer be ionized. The temperature was around 3000 kelvin. So now the universe is filled with primary Hydrogen and helium gas and it is transparent to light. So the glow of the hot matter was not absorbed and continued to travel.
The expansion of the universe has changed the wavelength of light from the visible spectrum to microwaves where we find it today.
The travel time of light to use depend on the distance to the source when it was emitted and the expansion of the universe. So the source for what we observe now is matter was at a distance so the travel time of the light is age of the universe minus approximately 379,000 years.
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