IAU Division I Working Group
``Nomenclature for Fundamental Astronomy'' (NFA)
Newsletter 6
Nicole Capitaine, 1 March 2005
Revised NFA Documents have been submitted to comments of the Members of the IAU Working Group
on "Nomenclature for Fundamental Astronomy" on 1 March 2005. They consist in
- updated NFA explanatory documents ,
- a draft IAU Resolution proposal reporting on the BCRS and GCRS orientation.
The NFA explanatory documents are intended to be transformed into the NFA Working
Group Report to the IAU with terminology recommendations.
Part B of these documents provides detailed implementation of the terminology proposed by
the Working Group. This part is composed of a chart for transformation from ICRS to observed
places (Part B1), a summary of terms and definitions (Part B2) and a terminology list (Part B3).
The latest revised versions of the B1, B2 and B3 documents represent a significant revision
of the previous versions.
This revision has resulted from: (i) the WG comments on previous versions of the documents,
(ii) the very active WG e-mail exchanges during the period July 2004-February 2005,
(iii) special efforts from Chopo Ma and Sergei Klioner in providing some of the
key definitions, (iv) fruitful discussions with Bernard Guinot and Patrick Wallace,
(v) the very efficient help by Catherine Hohenkerk in the preparation of the documents.
Some changes have been applied to the ITRS/ITRF definitions according to a Note by Claude Boucher
providing comments on this topic.
These documents are posted as html and will be regularly updated according
to the latest WG comments.
B1: Transformation Chart
B2: Summary of terms and definitions
B3: Terminology List
This draft IAU Resolution Proposal is intended to become the 2d part (Recommendation 2) of the NFA WG
recommendation that would be entitled "Supplement to the IAU 2000 Resolutions on reference frames"
to be submitted to the IAU as an IAU 2006 Resolution proposal. Recommendation 2 reports on the BCRS
and GCRS orientation that has been added to the IAU 2000 definition of BCRS and GCRS during the
recent WG discussion.
It will also be sumbitted by M. Soffel to the IAU Division 1 Working Group "Relativity in Celestial mechanics,
Astrometry and metrology" (RCMAM).
The first part (Recommendation 1) of the Resolution proposal on "Harmonizing the name of the pole and origin
to intermediate", on which the WG already agreed is included in the latest version of
the WG recommendations.
The second part is provided below.
The next step of the NFA WG work will be the preparation of Part A of the explanatory document,
which is intended to explain the basis for the IAU Resolutions and their implementation using the
terminology proposed by the WG.
Recommendation from
the Division 1 IAU Working Group
``Nomenclature for Fundamental Astronomy'' (NFA)
Supplement to the IAU 2000 Resolutions on reference frames
RECOMMENDATION 1. Harmonizing the name of the pole and origin to
``intermediate'': see the latest version of the WG recommendations
RECOMMENDATION 2. Default orientation of the BCRS and GCRS
(Preliminary Draft: 23 February 2005)
The XXVIth General Assembly of the IAU
NOTING
- (1)
- the adoption of resolutions IAU B1.1 through B1.9 by the IAU General Assembly
of 2000, and
- (2)
- that the International Earth rotation and Reference Systems service
(IERS) and the Standards Of Fundamental Astronomy (SOFA) activity have
made available the models, procedures, data and software to implement
these resolutions operationally, and that the Almanac Offices have begun
to implement them beginning with their 2006 editions, and
- (3)
- that, in particular, the systems of space-time coordinates defined
by IAU 2000 Resolution B1.3 for (a) the solar system (called the
Barycentric Celestial Reference System, BCRS) and (b) the Earth (called the
Geocentric Celestial Reference System, GCRS) have begun to come into use, and
- (4)
- the conclusions of the IAU Working Group on ``Nomenclature for
Fundamental Astronomy''
(A mention to the RCMAM WG should be added here)
RECOGNISING
- (1)
- that the BCRS definition does not determine the orientation of the
spatial coordinates,
- (2)
- that the natural choice of orientation for typical applications is
that of the ICRS,
- (3)
- that the GCRS is defined such that its spatial coordinates are
kinematically non-rotating with respect to those of the BCRS,
RECOMMENDS
- that, the BCRS definition is completed with the following: "For all
practical applications, unless otherwise stated, the BCRS is assumed to
be oriented according to the ICRS axes. The orientation of the GCRS
is defined by the ICRS-oriented BCRS."