Angular resolution describes the smallest angular separation or structure an observation can distinguish. A physical scale at distance subtends approximately radians when . Resolving a black-hole sphere of influence therefore involves distance as well as its physical radius, and useful kinematics also require adequate surface brightness.
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Angular resolution refers to the ability of an optical system, such as a telescope or microscope, to distinguish between two closely spaced objects. It is defined as the smallest angular separation between two points that can be resolved or distinguished by the system. In practical terms, a higher angular resolution means that the optical system can discern finer details at a given distance.