- Angular distance
mathematics(in particular geometryand trigonometry) and all natural sciences (including astronomy, geophysics, etc), the angular distance (angular separation, apparent distance, or apparent separation) between two point objects, as observed from a location different from either of these objects, is the size of the anglebetween 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).
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 a telescopes).
In order to calculate the angular distance in
arcsecondfor binary star system, extrasolar planets, solar system objects and other astronomical objects, we use orbital distance( semi-major axis) in AU divided by stellar distancein parsecs.
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