1. 3D representation of the Non-Rotating Origin Olivier de Viron and Veronique Dehant Royal Observatory of Belgium Scientific adviser: Nicole Capitaine

2. The Terrestrial Reference Frame

3. The Celestial Reference Frame

4. 2 systems in an ideal world

5. The less ideal world

6. TRF CRF Intermediate RS 1. polar motion in Earth 2. Earth rotation 3. Celestial motion of CIP Only the intermediate system is different when using the new or the old formalism. The definition of the TRF and CRF are not affected.

7. The old-version transformation

8. 1. From TRF to CIP

9. 2. To the True equinox of the date

10. How to go from one equinox another? Equator 1 Ecliptic 1  Ecliptic 2  Equator 2 x Z y

11. How to go from one equinox another? Equator 1 Ecliptic 1  Ecliptic 2 ii Z rotation 1 (z) x y x y

12. How to go from one equinox another? Equator 1 Ecliptic 2 ii x Z y y Z Rotation 2 (x)

13. How to go from one equinox to another? Equator 1 Ecliptic 2 ii Z  y x Rotation 4 (z) x Equator 2

14. How to go from one equinox to another? Ecliptic 2 Z  x Equator 2 Z Rotation 5 (x)

15. How to go from one equinox another? Ecliptic 2  x Equator 2 It took 5 successive steps…

16. True equator of the date Mean equator of the date Equator at J2000 Mean ecliptic of the date True ecliptic of the date Ecliptic at J2000 vv 00 1 2 3 4

17. The new transformation

18. 1. From TRF to CIP

19. 2. From the terrestrial NRO

20. 3. Earth Rotation Angle

21. 4. To the X CRF projection: s

22. 5. To CRF: celestial motion of the CIP

23. What is the NRO 2. Not a point in particular, any point of the CIP equator can work. 1. Characterized by its motion: no velocity around the CIP equator associated with polar motion or nutation. 3. Allows to get rid of the equinox in the change of reference frame.

26. So, we can take any points we want? 2. But, we want the new system to be consistent with the old one. 1. Yes, it is not the point it-self that matter, but its motion. 3. Thus, the point is chosen to insure continuity.

27. Conclusions The NRO is defined by its position at the base epoch (continuity) its motion (no motion in the CIP equator associated with polar motion). Only the Intermediate system is involved, no change of the CRF or TRF