The astrometric information in FITS images (also referred to as the WCS) is stored in the header using a standard set of keywords. The reference location is defined by the following keywords: . ... CD1_1 is the partial of first axis coordinate w.r.t. x . ... This facilitates proper translation of pixel to sky coordinates for science analysis, and allows for all the necessary shifting information for each image to be stored in the header of the image itself for future alignment reference. ...