Angular distance
Encyclopedia : A : AN : ANG : Angular distance
In mathematics (in particular geometry and trigonometry) and all natural sciences (including astronomy, geophysics, etc), the angular distance (or angular separation) between two point objects, as observed from a location different from either of these objects, is the size of the angle between the two directions originating from the observer and pointing towards these two objects. Angular distance (or separation) is thus synonymous to angle itself, but is meant to suggest the (often large or unknown) linear distance between these objects (for instance stars, as they are observed from Earth).
Measurement
Since the angular distance (or separation) is conceptually identical to an angle, all three are measured in the same units, such as degrees or radians, using instruments such as goniometers or optical instruments specially designed to point in well-defined directions and record the corresponding angles (such as telescopes).
See also
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