We simulate Planck observations by adopting a detailed model of the microwave sky including monopole, dipole, anisotropies of the cosmic microwave background (CMB) and galactic and extragalactic foregrounds. We estimate the impact of main beam optical aberrations on CMB anisotropy measurements in presence of extragalactic source fluctuations and we discuss the main implications for the Planck telescope design. By analysing the dipole pattern, we quantify the Planck performance in the determination of CMB spectral distortion parameters in presence of foreground contaminations.
