The angle subtended by an object at an observer. For a circular object of diameter viewed face-on at a distance much larger than , its angular diameter is approximately in radians.
An angular diameter inferred from the interferometric visibility of an extended source. The displayed monochromatic formula is for a uniformly bright circular disk, with projected baseline , diameter and wavelength . Its first visibility zero gives . Stellar angular diameter from a visibility envelope describes this calibration; real photospheres require limb-darkening corrections.
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Angular diameter (or angular size) is a measure of how large an object appears to an observer, expressed as an angle. It is typically measured in degrees, arcminutes, or arcseconds. Angular diameter is important in fields such as astronomy, where it helps to describe the apparent size of celestial objects (like stars, planets, and galaxies) from a specific point of view, typically from Earth or another observation point.