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ii. Geometrical inaccuracy(ies) introduced by optical, IR (infrared), or similar electromagnetic systems in which radiation is processed by mirrors. In optics, a specific deviation from perfect imagery (e.g., spherical aberration, coma, astigmatism, curvature of field, or distortion).
iii. The displacement of the apparent directions of the stars resulting from the motion of the observer. Also called an atmospheric aberration.