Circumference

The circumference of any circle or ellipse is the distance that a point on that circle or ellipse travels in a full circuit of it.

Mathematics
The formula for calculation of the circumference of any circle is:

c = π × d = 2 × π × r

where:

d is the diameter, r the radius and

π = 3.14159...

Astronomy
In astronomy the circumference of an orbit is the total distance through which an orbiting body displaces itself before arriving at the same orientation with respect to the primary and the fixed stars.