The Antarctic Circle's latitude fluctuates depending on the Earth's axial tilt, which changes due to tidal forces resulting from the orbit of the Moon.
 The other parameter is usually (1) the polar radius or semi-minor axis, b; or (2) the (first) flattening, f; or (3) the eccentricity, e
In geography, latitude is a coordinate that specifies the northsouth position of a point on the surface of the Earth or another celestial body

