Angular resolution

Angular resolution is the smallest angular separation at which an instrument can distinguish two sources as separate. It describes detail in angle rather than physical distance.

Rayleigh criterion: A diffraction-based rule for deciding when two point sources are just distinguishable. It gives a conventional threshold for the separation that counts as resolved.
Angular diameter: The angle subtended by an object's apparent width at an observer. It lets an object's apparent size be compared directly with an instrument's resolution.
Hubble Space Telescope: A space telescope launched in 1990 that observes ultraviolet, visible, and near-infrared light. Its location above the atmosphere supports sharp images at optical wavelengths.
Angular magnification: The ratio between an image's apparent angular size and an object's apparent angular size without an instrument. Magnification enlarges apparent detail but does not by itself resolve finer separations.
Diffraction limit: The finest detail an optical system can resolve because waves spread and interfere. It sets the fundamental resolution bound for an ideal aperture.
Arcsecond: An angular unit equal to one sixtieth of an arcminute, or 1/3,600 of a degree. Astronomical angular resolution is commonly reported in arcseconds.
Event Horizon Telescope: A global network of radio observatories that operates as an Earth-sized interferometer. Its long baseline enabled horizon-scale images of nearby supermassive black holes.
Sensitivity (electronics): A detector's ability to register weak signals or small changes in input. Sensitivity governs faint-source detection, not whether two sources can be separated.
Airy disk: The central bright spot and surrounding rings formed by diffraction through a circular aperture. Its width determines how much neighboring point images overlap.
Point source: An object whose apparent size is too small to distinguish from a point in a given observation. Resolution tests often ask whether two point sources remain distinct.

Linked from 25 pages