Astronomical annotations (also referred to as astrometric solving, plate solving, or astrometric calibration) is a technique or process where actual imaged stars are matched against astronomical catalogues to provide an annotated model of the objects photographed.
The astrometric calibrations used on this site (unless otherwise specified) are provided courtesy of Astrometry.com, which is a project supported by the US National Science Foundation, the US National Aeronautics and Space Administration, and the Canadian National Science and Engineering Research Council.