An Astronomer's View of the Pole.

Positional astronomers require a reference frame to which they can refer their observations, and which can be related, at any instant, to an inertial reference frame through dynamical theory. The exect definition of the celestial pole is of considerable practical importance, in order that proper allowance can be made for short period oscillations of observatory coordinates, and to avoid discontinuity in the reference frame as theories of the Earth's rotation are improved.
In this article the principles underlying the measurement of celestial coordinates are described, from the point of view of optical astronomy, and various complexities affecting the optimum definition of the 'ephemeris reference frame' are discussed. [ABSTRACT FROM AUTHOR]