In geometry, which unit is defined as being equal to the angle subtended at the centre of a circle by an arc equal in length to the radius ?
Radian circle by an arc that is equal in length to the radius of the circle. More generally, the magnitude in radians of such a subtended angle is equal to the ratio of the arc length to the radius of the circle; that is, , where "θ" is the subtended angle in radians, "s" is arc length, and "r" is radius. Conversely, the length of the enclosed arc is equal to the radius multiplied by the magnitude of the angle in radians; that is, . As the ratio of two lengths, the radian is a "pure number" that needs no unit
Circle of equal altitude Circle of equal altitude The circle of equal altitude also called circle of position, CoP, is the real line of position in celestial navigation. It is defined as the locus of the Earth on which an observer sees a star, at a given time, with the same observed altitude. The center of the CoP, is the substellar point or geographical position of the observed body, and its radius is the great circle distance equal to the zenith distance of the body. The equation links the following variables formula_1 Being "B" the latitude (+N/S), "L" the longitude (+E/-W). "LHA" = "GHA"