The purpose of this questionnaire is to provide information to the WG so that it can determine the opinions of the astronomical community regarding the terminology needed to implement and promulgate the IAU 2000 resolutions, including those on nutation and the new origin.

Questionnaire NFA/A is on the terminology choices. It is supported by a general presentation of the issue and an Annex providing a table of names, symbols, abbreviations and definitions, with possible alternatives.

Questionnaire NFA/B is for the Almanac Offices. The purpose is to provide information to the WG so that it can best help the Almanac Offices implement and promulgate the IAU 2000 resolutions, including those on nutation and the new origin, within the existing frame work

We appreciate all ideas, opinions, and concerns we receive, and we thank you for your time

 

 

1) Background in IAU Resolutions on reference systems

At its 23rd General Assembly in 1997, the IAU adopted the International Celestial Reference System (ICRS) as specified by IAU Resolution A4, 1991 and the International Celestial Reference Frame (ICRF) (Ma et al. 1998) that realizes the ICRS.  At the 24th IAU GA in 2000, a number of resolutions were passed that concern the definition of the astronomical reference systems and transformations between them, which are required when dealing with the Earth's rotation or when computing directions of celestial objects in various systems:

- Resolution B1.3 specifies that the systems of space-time coordinates as defined by IAU Resolution A4 (1991) for the solar system and the Earth within the framework of General Relativity are now named the Barycentric Celestial Reference System (BCRS) and the Geocentric Celestial Reference System (GCRS) respectively. It also provides a general framework for expressing the metric tensor and defining coordinate transformations at the first post-Newtonian level (see Soffel et al. 2003).

- Resolution B1.6 recommends the adoption of the new precession-nutation model that came into force on 1 January 2003 and is designated IAU 2000 (version A corresponding to the complete model of Mathews et al. (2002), of 0.2~mas accuracy and version B corresponding to its shorter version (McCarthy and Luzum 2002) with an accuracy at 1 mas level).

- Resolution B1.8 recommends the use of the ‘non-rotating origin’ (Guinot,1979), designated CEO (Celestial Ephemeris Origin) and TEO (Terrestrial Ephemeris Origin), as origins on the moving equator in the celestial and terrestrial reference systems, respectively, and defines UT1 as linearly proportional to the Earth Rotation Angle (ERA) between the CEO and the TEO on the moving equator.  This resolution recommends that the transformation between the International Terrestrial Reference System (ITRS) and the GCRS be specified by the position of the Celestial Intermediate Pole, CIP, (defined by Resolution B1.7) in the GCRS, the position of the CIP in the ITRS, and the ERA.  This resolution also recommends that the IERS continue to provide users with data and algorithms for the conventional transformations.

 

2) Terminology for Implementing the IAU Resolutions

The implementation of these Resolutions (especially B1.3, B1.7 and B1.8) for various astronomical applications requires that a consistent and well defined terminology is recognized and adopted by the astronomical community for all the quantities based on the new concepts.

The terminology issue began to be discussed in recent papers (Seidelmann and Kovalevsky 2002, Capitaine et al. 2003 a, b, c) and within the ICRS Working Group in 2003. This resulted in documents that were circulated and discussed within the WG ICRS before the last IAU General Assembly.

 

3) The Working Group ``Nomenclature for Fundamental Astronomy'' (NFA)

The IAU Working Group on NFA was created by Division I at the 24th IAU General Assembly in July 2003 and officially installed by the IAU in November 2003. The general task of this WG is to provide proposals for new nomenclature associated with the implementation of the IAU 2000 Resolutions and to make related educational efforts for addressing the issue to the large community of scientists. The webpage of the NFA WG is: http://syrte.obspm.fr/iauWGnfa/ where all the documents regarding the WG discussion and its Newsletters are posted, and includes those documents mentioned above.

 

4) The NFA Questionnaire

Based on (i) the document ``Draft of Nomenclature and Terminology for  the IAU WG'' by C. Hohenkerk (Annex 6 of Newsletter 1) and (ii) the preliminary list of questions about terminology provided in Newsletter 1, a draft questionnaire was prepared by C. Hohenkerk and submitted to the WG (November 2003). It has then been revised and completed (January 2004) based on the WG comments and suggestions and split into two parts, Questionnaire NFA/A on ‘terminology choices’ which is intended for the astronomical community and Questionnaire NFA/B for the Almanac Offices and related organizations.