Fig. 2

Annual mean zenith transmission curve for Cerro Paranal (black solid line). The Earth’s atmosphere extinguishes the flux from point sources by Rayleigh scattering by air molecules (red dash-dotted line), Mie scattering by aerosols (green dashed line), and molecular absorption (blue solid line). For the plotted wavelength range, the latter is caused by molecular oxygen (A band at 0.762 μm, B band at 0.688 μm, and γ band at 0.628 μm), water vapour (prominent bands at 0.72, 0.82, and 0.94 μm), and ozone (Huggins bands in the near-UV and broad Chappuis bands at about 0.6 μm).
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