Abstract: Two "non-rotating origins" were defined by the IAU in 2000 for the measurement of Earth rotation: the Celestial Ephemeris Origin (CEO) in the ICRS and the Terrestrial Ephemeris Origin (TEO) in the ITRS. Universal Time (UT1) is now defined by an expression based on the angle theta between the CEO and TEO. Many previous papers, e.g., Capitaine, Guinot, & McCarthy (2000), developed the position of the CEO in terms of a quantity s, the difference between two arcs on the celestial sphere. A similar quantity s was defined for the TEO. As an alternative, a simple vector differential equation for the position of a non- rotating origin on its reference sphere is presented here. The equation can be easily numerically integrated to high precision. This scheme directly yields the unit vector of the CEO in the ICRS, or that of the TEO in the ITRS, as a function of time. This simplifies the derivation of the main transformation matrix between the ITRF and the ICRS. The directness of the development may have pedagogical and practical advantages for the vast majority of astronomers who are unfamiliar with the history of this topic.
| Limitations: |
 APPROVED FOR PUBLIC RELEASE |
| Pages: |
5 |
| Report Date: |
22 JUL 2003 |
| Report Number: |
A822324 |
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