IAU WORKING GROUP
"Nomenclature for Fundamental Astronomy" (NFA)



Summary of the discussion on "Nomenclature in Fundamental Astronomy"

on Tuesday 21 September 2004, during the Journées 2004, Paris, 20-22 September 2004

(Nicole Capitaine, 2 November 2004)




This discussion took place (1700-1830) after Session III "Nomenclature in fundamental astronomy" chaired by D.D. McCarthy and including the following contributions:

The following points were introduced by the panel, composed of N.Capitaine, C.Hohenkerk, C.Ma, D.McCarthy, M.Soffel and P.Wallace, and were submitted to the audience for comments and discussion:

       (1) The draft NFA WG recommendations

       (2) The draft Resolution proposal to the IAU 2006 GA

       (3) The WG explanatory documents

       (4) Future actions of the NFA

The discussion on these points is summarized below.

(1) The draft NFA WG recommendations

The discussion concluded by supporting Recommendations 1 to 12, except for, in Recommendation 9, the comment on the use of Greenwich meridian which was considered unnecessary by a number of participants.

The most contentious points in the other recommendations were: The conclusion on the system/frame question was using "system" in the broadest sense as possible (especially in the case of the intermediate system), but keeping "frame" for the set of coordinates as with the ICRF; a suggestion by M. Soffel to suppress the use of "frame" was debated but not supported, especially because of the necessity of having ITRF in the terrestrial case. Using special designations for particular realizations of the "intermediate celestial system" was supported, but not for the ICRS or ITRS which are considered as being theoretical ideal versions of the ICRF and ITRF, respectively, although a certain asymmetry was recognized between the celestial and terrestrial cases (e.g. special designations exist for the ITRF, such as ITRF2000, but not for the ICRF).

In Recommendation 12, there was the requirement that "ITRF prime meridian" be replaced by "ITRF zero-meridian" which was to be verified, and agreed afterwards, by the ITRS IERS Product Center (C. Boucher).

(2) The draft Resolution proposal to the IAU 2006 GA

This proposal was supported, except by one participant who was strongly against.

(3) The WG explanatory documents


(4) Future actions of the NFA

Further educational efforts were strongly recommended. Part A of the NFA explanatory document is considered as being a key document to be realized by the WG. The 3D representation of the Non-Rotating Origin presented by O. de Viron will be made available (through a link to the appropriate URL) after some improvements on the NFA web page.

(*) More recent discussions with Sergei Klioner during the GAIA meeting in Meudon, leads me to think, that in this case, we can assume in addition, that the BCRS considered here, has its spatial axes fixed to those of the ICRS; this would avoid having to introduce a new name for the GCRS that has its axes aligned to those of the ICRS.