Angular distance
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angular distance
(′an·gyə·lər ′dis·təns)
(mathematics) For two points, the angle between the lines from a point of observation to the points. The angular difference between two directions, numerically equal to the angle between two lines extending in the given directions. The arc of the great circle joining two points, expressed in angular units.
(physics) The distance between two points, expressed in wavelengths at a specified frequency.
Oxford Dictionary of Sports Science & Medicine:
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angular distance
1. The sum of all the angular changes that occur during the rotation of a body.
2. The distance between two bodies measured in terms of the angle subtended by them at the point of observation.
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Angular distance
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In mathematics (in particular geometry and 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 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).
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Measurement
Since the angular distance (or separation) is conceptually identical to an angle, it is 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).
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In order to calculate the angular distance in arcseconds for binary star system, extrasolar planets, solar system objects and other astronomical objects, we use orbital distance (semi-major axis) in AU divided by stellar distance in parsecs.
See also
References
- Weisstein, Eric W., "Angular Distance" from MathWorld.
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Oxford Dictionary of Sports Science & Medicine
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