Geometric interpretation of the Frenet-Serret frame description of circular orbits in stationary axisymmetric spacetimes

A geometrical interpretation is given for the Frenet-Serret structure along constant speed circular orbits in orthogonally transitive stationary axisy mmetric spacetimes. This gives a simple visualization of the acceleration o f these orbits and of the Fermi-Walker angular velocity of the usual symmet ry-adapted frame vectors along them and provides an elegant description of the various observers characterized by critical values of the variables par ametrizing the acceleration.