Page "Cosmic microwave background radiation" Paragraph 14

The detail analysis of CMBR data to produce maps, an angular power spectrum, and ultimately cosmological parameters is a complicated, computationally difficult problem.

Although computing a power spectrum from a map is in principle a simple Fourier transform, decomposing the map of the sky into spherical harmonics, in practice it is hard to take the effects of noise and foreground sources into account.

In particular, these foregrounds are dominated by galactic emissions such as free-free, synchrotron, and dust that emit in the microwave band ; in practice, the galaxy has to be removed resulting in a CMB map that is not a full-sky map.

In addition, point sources like galaxies and clusters represent another source of foreground which must be removed lest they distort the short scale structure of the CMB power spectrum.