天球和地球历书原点

国际天球参考系的使用、观测精度的提高和方法的改善要求采用与地球轨道运动无关的运动赤道上的起算点，Guinot提出的非旋转原点可作为这样一种选择。非旋转原点依赖于天球参考极。IAU决定从2003年起采用天球中间极作为天球参考极。非旋转原点在天球参考系的使用，可给出在天球中间极赤道上的天球历书原点，非旋转原点在地球参考系的使用，可给出在天球中间极赤道上的地球历书原点。回顾了非旋转原点的概念、以历书原点为参考的天球参考系和地球参考系的坐标变换，经出了在微角秒精度下天球参考极的坐标和历书原点的位置，讨论了采用历书原点对测定UT1的影响，指出当岁差章动模型、天极补偿、分点改正得到改善时，基于历书原点的UT1定义不需要更改，从而保证了UT1的连续。

Celestial and Terrestrial Ephemeris Origins

The adoption of the International Celestial Reference System and the changes of observational strategy call for the use of departure point on the moving equator independently from Earth's orbital motion. A Nonrotating Origin (NRO), proposed by Guinot, is selected. It de- pends on the celestial reference pole. IAU will adopt the Celestial Intermediate Pole (CIP) as the celestial reference pole from 1 January 2003. The use of NRO in the Celestial Reference System (CRS) is designated as the Celestial Ephemeris Origin (CEO). The use of NRO in the Terres- trial Reference System (TRS) is designated as the Terrestrial Ephemeris Origin (TEO). In this paper, the concept of the NRO, the coordinate transformation between the CRS and the TRS are reviewed, the coordinates of the celestial reference pole and the positions of the ephemeris origins at a microarcsecond accuracy are provided, the influence on the determination of UT1 of errors in the precession-nutation model, when the ephemeris origins axe used, is discussed. The results show the definition of UT1 based on the ephemeris origins does not require modifications in order to maintain the continuity of UT1 when the models for precession-nutation, pole offset and equinox correction are improved.