The distance between two objects, measured in terms of the angle between them at the point of observation.
the angular separation between two objects as perceived by an observer; "he recorded angular distances between the stars"
Angular distance is the measure of an arc (a segment of the circumference of a circle). Angular distance measures the proportion of a circle that the arc in question consists of. Angular distance is expressed in degrees, radians, arc minutes (one-sixtieth of a degree), or arc seconds (one-sixtieth of a minute). For example, latitude is the angular distance north or south of the equator measured in degrees, and longitude is the angular distance east or west of the prime meridian (which goes through Greenwich, England), measured in degrees.
The apparent distance between two celestial objects. It is measured in degrees, arcminutes and arcseconds. On average, the distance from your thumb tip to the tip of your little finger of your outstretched hand at arms length is 20 degrees. The width of your palm will be about 12 degrees and the width of the tip of your little finger is about 1 degree. The angular diameter of the Moon (and the Sun) is more or less 1/2 degree. Aperture The diameter of the main lens or mirror of a telescope. Aphelion When something is orbiting the Sun, this is the point of the orbit that is furthest from the Sun. See also perihelion. Apogee When something is orbiting the Earth, this is the point of the orbit that is furthest from the Earth. See also perigee.
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).