Recognizing the cosmological importance of the darkness of the night sky (Olbers' paradox) and the first speculations on an extragalactic background light dates back to the first half of the 19th century.
Despite its importance, the first attempts were made only in the 1950-60s to derive the value of the visual background due to galaxies, at that time based on the integrated starlight of these stellar systems.
Later the discovery and observations of high luminosity infrared galaxies in the vicinity of the Milky Way showed, that the peak of the CIB is most likely at longer wavelengths (around 50μm), and its full power could be ~1−10% of that of the CMB.
He also pointed out, that the CIB cause a significant attenuation for very high energy electrons, protons and gamma-rays of the cosmic radiation through inverse Compton scattering, photopion and electron-positron pair production.
Nuclear fusion takes place inside the stars, and we can really see this light redshifted: this is the main source of the cosmic ultraviolet- and visual background.
Galaxy collisions and mergers were more frequent in the cosmic past: the global star formation rate of the Universe peaked around redshift z = 1...2, and was 10 to 50 times the average value today.
In these systems most of the gravitational potential energy of the matter falling into the central black hole is converted into X-rays, which would escape unless they are absorbed by the dust torus of the accretion disc.
A hitherto unrecognised population of intergalactic stars have been shown to explain the CIB as well as the other elements of the diffuse extragalactic background radiation.
If intergalactic stars were to account for all of the background anisotropy, it would require a very large population, but this is not excluded by observations and could in fact also explain a fair part of the dark matter problem as well.
It also lacks suspicious spectral features, since the final shape of its spectrum is the sum of the spectra of sources in the line of sight at various redshifts.
In practice, one needs an instrument that is able to perform absolute photometry, i.e. it has some mechanism to fully block incoming light for an accurate zero level determination (cold shutter).
The infrared surface brightness of the Galactic cirrus must correlate with the neutral hydrogen column densities, since they originate from the same, low-density structure.
Later, short-wavelength DIRBE measurements at 2.2 and 3.5μ were combined with the Two Micron Sky Survey (2MASS) source count data, and this led to the detection of the CIB at these two wavelengths.
[6] In the far-infrared the CIB power spectrum can be effectively used to separate it from its strongest foreground, the Galactic cirrus emission.
The source count results exclude the "steady state" scenarios, where z=1...2 galaxies look similar to those we see today in our cosmic neighborhood.