$\star$ Not or far from basic of sky

As we saw, the principal contribution to the errors of flux on the ground are the contributions of the light of the bottom of sky. Even if there remains a bottom of residual sky (in particular the light zodiacale ), the contributions of the bottom of sky are in practice of the same order of magnitude as the noise of reading of CCDs.

In the case of an object with great flux, the aperture photometry is thus the optimal method.

The study of the objects with small fluxes require as for it more detailed study, the estimate of the noise must take into account the three contributions: sky, the flux of the object and noise of reading which have contributions of the same order of magnitude. In this case, the estimate must be carried out by using equation Contents