Power spectra of six fields observed by both Planck (red) and Herschel (black). Fits to the spectra are shown in blue. There is a good agreement between Planck and Herschel in the common multipole range (typically ℓ< 3000). Fields are, from top to bottom: (a) Aquila; (b) Polaris; (c) Spider; (d) Draco; (e) Gama; (f) FLS; and (g) XMM-LSS. No real Galactic sources are expected in fields (b)–(g), only extragalactic sources (correlated and Poisson components) and cirrus at larger angular scales. Real Galactic sources are detected, however, in (a) (André et al. 2010): the power spectrum is orders of magnitude above the other fields, demonstrating the need to separate the Galactic from extragalactic zones, and the use of the background brightness as a proxy to estimate the cirrus contamination.