Spatial Resolution of the Measurement of the Location of A Star Carried out by Means of the Gravity Center Method When A CCD Is Used During the Observation and the Effects of the Flat Correction, Sky Background and Noise——A Method of Astronomical Measurements with CCDs(Ⅱ)

The effects of the sky background, flat correction and noise on the measurement of the location of a star by means of the gravity center method centering by means of the method of weighten center arc theoretically analysed in this paper. The corresponding error formulas are also presented quantitatively. According to the characteristics of the discreteness of CCD images, the relation between the resolution and the size of a stellar image is derived, thereby proving that the accuracy of the measurement of the stellar image by means of the gravity center method may reach to a few percent of a pixel.The measuring error of the spatial resolution with the No.1 CCD receiving system of theYunnan Observatory is less than 0.1 arc secnod according to a conversative estimation.