Left: frequency spectra of individual diffuse foregrounds at high galactic latitudes, estimated at ℓ = 200, the angular scale at which CMB fluctuations are greatest and foreground fluctuations are relatively the least important (see Fig. 27). The horizontal line gives the level of the CMB. Right: angular power spectra of various foregrounds at 100 GHz, along with the best-fit Planck CMB spectrum. In both panels, solid lines show where the spectra are estimated from data, and dashed lines are extrapolations.