Observations of the Celestial Ephemeris Pole

• Published in: Highlights of Astronomy
• Main Author: Gross, R.S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1995
• Subjects: General Medicine; North Pole
• Online Access: http://dx.doi.org/10.1017/s1539299600011084; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1539299600011084

Abstract Space-geodetic measurement systems are capable of determining: (1) a terrestrial, body-fixed reference frame defined in practice by the stated positions and secular motions of a set of observing stations, (2) a celestial, space-fixed reference frame defined in practice by the stated locations of celestial objects, and (3) the rotation parameters linking these two frames together. Five parameters are conventionally used to specify the orientation of the terrestrial frame with respect to the celestial frame: two nutation parameters, two polar motion parameters, and one spin parameter. The celestial ephemeris pole (CEP) is defined as the north pole of that axis about which the spin parameter (UT1) is measured. The two nutation parameters locate the CEP in the celestial frame, and the two polar motion parameters locate the CEP in the terrestrial frame. By examining the frame transformation matrices, an expression relating the location of the rotation pole to that of the CEP can be derived. In order to compare theoretical predictions with observations, results of models for the effect on the nutations of geophysical excitation processes such as diurnal oceanic current and sea level height variations should not only be given in terms of the location of the CEP (rather than of the rotation pole), but must also account for the resonance effects of the free core nutation.