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). Euclid, Greek mathematician, 3rd century BC, known today as the father of geometry; shown here in a detail of The School of Athens by Raphael. ...
Table of Geometry, from the 1728 Cyclopaedia. ...
Wikibooks has a book on the topic of Trigonometry Trigonometry (from the Greek trigonon = three angles and metron = measure [1]) is a branch of mathematics which deals with triangles, particularly triangles in a plane where one angle of the triangle is 90 degrees (right triangles). ...
The lunar farside as seen from Apollo 11 Natural science is the rational study of the universe via rules or laws of natural order. ...
This article is about angles in geometry. ...
## 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 a telescopes). The definition, agreement and practical use of units of measurement have played a crucial role in human endeavour from early ages up to this day. ...
A degree (in full, a degree of arc, arc degree, or arcdegree), usually symbolized Â°, is a measurement of plane angle, representing 1ï¼360 of a full rotation. ...
The radian is a unit of plane angle. ...
A goniometer is an instrument that either measures angles or allows an object to be rotated to a precise angular position. ...
50 cm refracting telescope at Nice Observatory. ...
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