A CCD Detector Attached to the Lower Latitude Meridian Circle——(Ⅲ) Several Correction for the Spherical Astronomy

In this paper, the curvature correction, which should be added to the determined value of the zenith distance in the meridian direction, and the corresponding corrections of the time, of a star's passage across the prime vertical direction and of the determined value of the zenith distance arc derived by means of the, method of the projection ellipse. The influence of the variation in the angle between the projection of the right ascension circle of an object and the meridian plane on the determined value of the measured coordinate x during the observation of the star carried out in the meridian direction is also derived. The corrections and influence arc all caused by the observation of the star by rotating the horizontal axis and by the deviation of the image of the star from the relative center of the CCD chip. In addition, the differen-tial corrsctions of the atmospheric refraction and annual aberration of the image of a tar in the field of view with respect to the relative center of the chip are also derived and the correction formula with 1/2(x'-x) and 1/2(y'-y) as the variables are given. And a conclusion is drawn that the differential correction of the atmospheric refraction may be neglected if the observation of stars is carried out when the zenith distance is greater than 15°.