CCD Photometry: Measurement uncertainity

Aperture photometry is one of the methods which allows to measure intensity of a star on a CCD frame. There exist several programs which can be used for this, such as DAOPHOT, MuniPack, C-MuniPack. If we use any method for data processing, it is very important to know how the method works. In this paper we discuss how it measures the brightness of a star. However, the knowledge of stellar brightness is insufficient because each measurement has an error. We discuss also in this paper the simply method how can be estimate the measurement uncertainty. Above mentioned codes use this method. It is based on aperture photometry used to stellar brightness estimation and on the using of statistics. It does not require complicate calculations or additional measurements. Brightness and its uncertainty are determinate only from the CCD frame.