In geometry, an arc is a closed segment of a differentiable curve in the two-dimensional plane; for example, a circular arc is a segment of the circumference of a circle. If the arc segment occupies a great circle (or great ellipse), it is considered a great-arc segment.
Substituting in the circumference
and solving for arc length, , in terms of yields
For an angle measured in degrees, the size in radians is given by
and so the arc length equals then