Sky Brightness given by the User

The observer can set a brightness of the sky in ${\frac{{\mathrm{mag}(\mathrm{VEGA})}}{{\Box \mathrm{arcsec}}}}$ for the zenith. It is the brightness of the sky for the filter used for the observation. The Airmass (AM) scales the number of photons from the sky background with

(- 0.000278719 ^. AM ^. AM ^. AM - 0.0653841 ^. AM ^. AM + 1.11979 ^. AM - 0.0552132)