1 Arcsecond:1 Arcsecond is equal to exactly one thirtysix-hundredth arc degrees (1°/3600). In terms of radians (SI unit) this is π/648000 rad or approximately 4.848 137 x 10-6 rad.
Circle:A circle is a simple closed shape. It is the set of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves so that its distance from a given point is constant. The distance between any of the points and the centre is called the radius.