Recommendation concerning the Celestial Ephemeris Pole
IAU Colloquium 180 "Towards Models and Constants for Sub Microsecond Astrometry"
Noting the need for accurate definition of reference systems brought about by unprecedented observational precision, and
Recognizing that it is necessary to abandon the conceptual definition of the Celestial Ephemeris Pole as the pole that has no nearly diurnal motion,
Recommends
1. that the Celestial Ephemeris Pole be the pole of the equator the motion of which with respect to the International Celestial Reference System is produced by external gravitational forces acting on the Earth,
2. that at J2000.0 the direction of the Celestial Ephemeris Pole be coincident with the direction of the International Celestial Reference Pole at
J2000,
3. that the direction of the Celestial Ephemeris Pole in the International Celestial Reference System at any epoch be defined in part by a nutation
model containing only predictable components of nutation with periods greater than two days,
4. that the motion of the Celestial Ephemeris Pole in the International Celestial Reference System be speci ed by:
a precession/nutation formulation designated as the MHB000 model plus
b additional corrections provided by the International Earth Rotation Service through appropriate astrogeodetic observations plus
c the geodesic nutation and
5. that the motion of the Celestial Ephemeris Pole in the International Terrestrial Reference System be provided by the International Earth Rotation Service
through appropriate astrogeodetic observations.
Recommendation concerning the Celestial Ephemeris Origin
IAU Colloquium 180 "Towards Models and Constants for Sub Microsecond Astrometry"
Recognizing the need for reference system definitions suitable for modern observational accuracy,
Recommends
1.that the Celestial Ephemeris Origin of the International Celestial Reference System be the non-rotating origin, and
2. that the time scale UT1 be defined as being proportional to the Earth Rotation Angle defined by the angle measured along the equator between the direction
of the International Terrestrial Reference Origin and the Celestial Ephemeris Origin.
Recommendation concerning the the transformation between Terrestrial and Celestial Reference Systems
IAU Colloquium 180 "Towards Models and Constants for Sub Microsecond Astrometry"
Noting the need for accurate definition of reference systems brought about by unprecedented observational precision,
Recommends
that the transformation between the Terrestrial and Celestial Reference Systems be specied by the position of the Celestial Ephemeris Pole in the
Celestial Reference System, the position of the Celestial Ephemeris Pole in the Terrestrial reference System, and the Earth Rotation Angle defined by
the angle measured along the equator between the direction of the Terrestrial Reference Origin and the Celestial Ephemeris Origin.