1. An attitude determination system for an artificial satellite, comprising: an image processor for processing star images which are observation values of stars sensed at predetermined time points by a star sensor mounted on said artificial satellite to arithmetically determine direction vectors of said observed stars; a rotation estimator for estimating a rotational motion between an attitude of said artificial satellite at a predetermined time point and an attitude of said artificial satellite at another time point; an elongation estimator, having an output of said rotation estimator and an output of said image processor as its inputs, which estimates elongations between the direction vectors of said observed stars on the basis of said estimated rotational motion; a star identifier for establishing correspondences between a plurality of the stars for which relation of said elongations has been determined and stars on a star catalog; and an attitude angle estimator for estimating an attitude angle of said artificial satellite on the basis of result of the identification of the stars, wherein said rotation estimator uses the star images on a plurality of image screens respectively photographed at different image pick-up time points by said star sensor.