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Annexes to Newsletter 1
The membership is:
Nicole CAPITAINE (Paris Observatory, France):
Chair
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, and that the IERS continue to provide
users with data and algorithms for the conventional transformations.
The WG should have to agree on the final terminology
to adopt.
The terminology has to be selected in the two
official languages of the IAU (English and French), with possible compatibility
with other languages.
The use of capitals has to be questioned (see
Annex 6) for the new terms such as ``Earth Rotation Angle'', whereas lower
case is used (except for the first letter of the first word) for classical
terms such as ``Greenwich sidereal time''.
One choice (Choice A) can be to use a terminology
based on an approach similar to the classical one. Example ``the equation
of the equinoxes'' ``the equation of the origins'' (See Annex 6).
An other choice (Choice B) can be not to rely
on an approach similar to the classical one, but rather to try to be as
close as possible to the concept.
The following list, that should have to be extended
to all the relevant quantities, provides several choices for each quantity
corresponding to one concept1.
PRELIMINARY LIST OF TERMINOLOGY CHOICES (as an
example) 1. Origin on the equator of the CIP with
respect to the GCRS (cf Annex 4)
2. Origin on the equator of the CIP with respect
to the ITRS (cf Annex 4)
3. Equatorial longitude
4. Angular distance between the equinox and
the CEO
Capitaine, N., Wallace, P.T, McCarthy, D.D., 2003b,
``Expressions to implement the IAU 2000 definition of UT1'', Astron.
Astrophys. 406, 1135-1149.
Capitaine, N., Wallace, P.T, Chapront, J., 2003c,
``Expressions for IAU 2000 precession quantities'', Astron. Astrophys.
, in press.
Guinot, B., 1979, in Time and the Earth's Rotation,
D.D. Mc Carthy, J.D. Pilkington (eds), D. Reidel Publishing Company, pp.
7-18.
IERS Conventions 2000, http://www.usno.mil/Conventions
2000, draft
Ma, C.,Arias, E.F., Eubaks, M. Fey, A.L., Gontier,
A.-M., Jacobs, C.S., Archninal, B.A., Charlot, P., 1998, ``The International
Celestial Reference Frame as realized By Very Long Baseline Interferometry,"
Astron. J.
116, 516-546.
Mathews, P. M., Herring, T. A., and Buffett B.
A., 2002, ``Modeling of nutation-precession: New nutation series for nonrigid
Earth, and insights into the Earth's Interior," J. Geophys. Res.,
107, B4, 10.1029/2001JB000390.
McCarthy, D. D. and Luzum, B. J., 2002, ``An Abridged
Model of the Precession-Nutation of the Celestial Pole," Celest. Mech.
85, 35-49.
Seidelmann, P. K., Kovalevksy, J., 2002, ``Application
of the new concepts and definitions (ICRS, CIP and CEO) in fundamental
astronomy," Astron. Astrophys. 392, 341-351.
Soffel, M., Klioner, S.A., Petit, G. et al. 2003,
``The new IAU Resolutions for astrometry, celestial mechanics and metrology
in the relativistic framework: explanatory supplement'', Astron. J.
in press.
Annex 1:``The new reference Systems: some answers''
(K. Seidelmann), March 2003.
Annex 2: Suggestions for improving the previous
document (M. Soffel and S. Klioner), April 2003
Annex 3: ``Implementation of the IAU 2000 precession-nutation
and Universal Time using the new paradigm. Summary for the Division 1 ICRS
Working Group and Commission 19 Precession-Nutation Working Group'' (N.
Capitaine, P. Wallace, D.D. McCarthy, J. Chapront), February 2003
Annex 4: Project of an IAU resolution, WG ICRS,
April 2003
Annex 5: Report of Division I meetings at the
XXV IAU GA (N. Capitaine), October 2003
Annex 6: Draft of Nomenclature and Terminology
for the IAU WG (C. Hohenkerk), October 2003
Copyright © 1993, 1994, 1995,
1996,
Nikos Drakos,
Computer Based Learning Unit, University of Leeds.
The command line arguments were:
Introduction
The present Newsletter of the Working Group ``Nomenclature
for Fundamental Astronomy'' (NFA) provides its task and composition and
a preliminary discussion on the current situation and questions relevant
to the WG. A method for organizing the work within the WG is proposed.
Task of
the Working Group
The general task of this Working group 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 a large community of scientists.
Composition
of the Working Group
The members of this WG include, as recommended by
the Division I Board, (i) promoters of IAU Resolutions 2000, (ii) experts
in the different fields of importance for the task of the WG (i.e.
Standards and Conventions, Relativity, star catalogues, etc.) and (iii)
Commission 5 ``Documentation and Astronomical Data'' representative.
Toshio FUKUSHIMA (NAO, Japan, Division I President):
ex officio
Bernard GUINOT (Paris Observatory, France): IAU
2000 Resolutions
Catherine HOHENKERK (HMNAO, UK): Almanac
George KAPLAN (USNO, USA): Implementation
and educational efforts
Sergei KLIONER (Lohrmann Observatory, Germany):
Relativity
Jean KOVALEVSKY (OCA, France): IAU 2000 Resolutions
Irina KUMKOVA (IAA, Russia): Star Catalogues
Dennis D. MCCARTHY (USNO, USA): IERS Conventions
Ray NORRIS (CSIRO, Australia): Commission
5 representative (to be confirmed)
Ken SEIDELMANN (Virginia University, USA): IAU
2000 Resolutions
Patrick WALLACE (HMNAO, UK): Standards Of
Fundamental Astronomy
The IAU
2000 Resolutions
At its 23rd General Assembly in 1997, the IAU adopted
an International Celestial Reference Frame (ICRF) (Ma et al. 1998) that
realizes the International Celestial Reference System (ICRS), as specified
by IAU Resolution A4, 1991. Several resolutions were adopted by the 24th
IAU General Assembly (Manchester, August 2000) that concern the definition
of the astronomical reference systems and transformations between them,
which are required when dealing with Earth's rotation or when computing
directions of celestial objects in various systems.
Terminology
for Implementing the IAU Resolutions
The implementation of these Resolutions (especially
B1.3, B1.7 and B1.8) for various astronomical applications require that
a terminology is adopted by the astronomical community for all the quantities
based on the new concepts. The terminology issue has begun to be discussed
in recent papers (Seidelmann and Kovalevsky 2002, Capitaine et al. 2003
a, b, c) and within the Working Group ICRS before the latest IAU General
Assembly resulting in the following documents that were circulated and
discussed within the WG ICRS on the first term of 2003:
Then, at the XXV IAU General Assembly in Sydney,
there has been a discussion on the ``Implementation of the IAU Resolutions
for the Almanacs'' during the Division I meetings on which a report (Annex
5) will be published in IAU Transactions XXV B. The conclusion of this
discussion has been that:
The discussion made it clear that the educational
effort would be easier if ``intermediate'' was used for both the ``Celestial
Intermediate Pole'' (CIP) and the ``Celestial Intermediate Origin'', instead
of ``Celestial Ephemeris Origin'', thus providing the ``Celestial Intermediate
Frame'', as it was in the recent project of IAU Resolution. Note that the
reason for not having adopted the expression ``Intermediate Origin'' in
the IAU 2000 Resolution was for avoiding a possible confusion with the
acronym CIO, used in the past for the ``Conventional International Origin''
for polar motion. To overcome this difficulty, a different font could be
proposed, as for the previously used acronym, the normal one being kept
for the Celestial intermediate origin.
Terminology
for the Almanacs
The implementation of the IAU Resolutions has to
be finalized within one year to be effective in the 2006 Almanacs. A preliminary
document has been prepared by C. Hohenkerk with a list of terms that have
to be chosen for the implementation in the Almanacs (Annex 6) together
with relevant questions.
Educational
effort
An educational effort is needed for addressing the
issue of the new system to a large community of scientists who want basic
concepts, background, justification, and some assessment of the effect
the changes will have on their work. This requires to provide practical
information and background material and provide basic explanations of the
ICRS, BCRS, GCRS, transformation between space-time coordinates, non-rotating
origin concept, and other aspects of the IAU 2000 resolutions. The preliminary
IERS educational effort in making available to users an initial set of
frequently asked questions on the recent IAU resolutions, has to be extended
and addressed to a wider community.
Preliminary
list of questions about terminology
Given the astronomical quantities that have to be
defined based on the new concepts (see for ex Annex 6), a preliminary terminology
list can be provided including, for each definition, the involved concept
and several choices for the corresponding quantity.
(1) Celestial ephemeris origin (CEO), (2) Celestial
intermediate origin (CIO), (3) other
(1) Origine céleste des éphémérides
(CEO), (2) Origine céleste intermédiaire (CIO), (3) autre
(1) Terrestrial ephemeris origin (CEO), (2) Terrestrial
intermediate origin (TIO), (3) other
(1) Origine terrestre des éphémérides,
(2) Origine terrestre intermédiaire (TIO), (3) autre
(1) CEO right ascension, (2) intermediate right
ascension, (3) other
(1) Ascension droite CEO, (2) Ascension droite
intermédiaire, (3) autre
(1) instantaneous origin distance, (2) equation
of origins, (3) other
(1) distance des origines instantanées,
(2) équation des origines, (3) autre
Organization
of the Work of the Working Group
The proposed work of the Working Group NFA is:
The proposed organization of the work is the following:
References
Capitaine, N., Chapront J., Lambert, S., Wallace,
P.T, 2003a, ``Expressions for the coordinates of the CIP and the CEO using
the IAU 2000 precession-nutation model,"Astron. Astrophys. 400,
1145-1154.
List of
Annexes
All the Annexes are available on the Working Group
webpage (at: http://syrte.obspm.fr/iauWGnfa): Annexes 1, 2 and 4 as Word
files, Annexes 3 and 5 as PS files and Annex 6 as PDF file.
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