Standards Of Fundamental Astronomy

This paper was given at the 1997 August IAU General Assembly in Kyoto, Japan, by Patrick Wallace.



At its 1994 General Assembly, the International Astronomical Union resolved to introduce new arrangements to establish and maintain an accessible and authoritative set of constants, algorithms and procedures that implement standard models used in fundamental astronomy. The initiative was the responsibility of the Working Group on Astronomical Standards (WGAS), part of Division 1 of the IAU, and the set of procedures and constants was named SOFA, for ``Standards Of Fundamental Astronomy''. The background to the IAU Resolution is given by Fukushima (1995) and Wallace (1996).

The proposed scheme includes the following elements:

The present status of the SOFA scheme is that the Reviewing Board has been set up, the site for the Distribution Center has been identified, and preliminary software work is underway.

The SOFA Review Board

In 1995 February, the author was invited by the WGAS to chair the SOFA reviewing board (which has since become known as the ``SOFA Review Board''). A process of consultation then took place, clarifying various aspects of the SOFA initiative itself and the role of the Board. This led to an announcement inviting the nomination of candidates for Board membership, in IAU/WGAS Circular 104, 1995 November. By 1996 February, the Board's membership had been agreed, and ratified by the WGAS and its Advisors. The current Board membership is as follows:

 Wim Brouw 		 Australia Telescope National Facility

 Anne-Marie Gontier 	 Paris Observatory

 Catherine Hohenkerk 	 Royal Greenwich Observatory

 Wen-Jing Jin 		 Shanghai Observatory

 George Kaplan 		 United States Naval Observatory

 Zinovy Malkin 		 Inst. Appl. Astron., St Petersburg

 Dennis McCarthy 	 United States Naval Observatory

 Jeffrey Percival 	 University of Wisconsin

 Patrick Wallace 	 Rutherford Appleton Laboratory

As a by-product of the trawl for Board members, a number of individuals were identified who were prepared to act as ``reviewers'' of new SOFA products.

With no independent funding, the SOFA Review Board relies on the host institutions of its members to provide the necessary resources. SOFA's needs in terms of computer facilities have, at least up to now, been modest, and easily met by existing equipment. Effort is, and is likely to remain, the most serious bottleneck. A further constraint is funding for travel. The bulk of the Board's work so far has been carried out by electronic mail, and this will continue. However, two meetings have also taken place, and most Board members were able to attend at least one of them. The first meeting was at USNO in 1996 September, followed a month later by one held at the Paris Observatory.

In the months leading up to the Washington and Paris meetings, discussion via electronic mail had produced a measure of agreement on various matters of detail, and a draft Fortran coding standard had been prepared. The meetings allowed this work to be consolidated, and significant further progress was made. Among the decisions reached were:

The SOFA Center

The Announcement of Opportunity for institutions to bid to become the SOFA Center was published at the beginning of 1997, in IAU Bulletin 79 and elsewhere. By the 1997 April 30 deadline, two bids had been received, from Rutherford Appleton Laboratory and the United States Naval Observatory respectively. In 1997 June (with representatives of the two bidding institutions excluded from the voting) the Board endorsed RAL as the SOFA Center.

The SOFA Center will be operated in parallel with the Starlink service and will employ the same techniques as Starlink's ``Software Store''. This is a self-service facility, enabling enquirers to obtain software and documentation directly through the World Wide Web. The Web is expected to remain the principal medium for disseminating SOFA products; however, supplementary distribution services using magnetic, optical or printed media may also be introduced if there is a demand.

It is intended that the service provided by the SOFA Center will be monitored by a management board. This board will present reports and assessments at each triennial General Assembly of the IAU. The management board will initially be the WGAS. Because IAU Working Groups exist only for a limited period, it will be necessary in due course to establish a permanent SOFA Management Board, perhaps in the form of a new IAU Commission. Steps to bring about this change will be taken prior to the IAU General Assembly in 2000.

The First SOFA Algorithms

Apart from the ``toolkit'' routines, the following set of algorithms will be the first SOFA products to appear:

The great care with which the SOFA routines will have to be designed and evaluated means that rapid progress cannot be expected, and it is likely to take several years to provide even this basic set. However, successive refinements of existing models, such as new precession and nutation series, will be relatively easy to introduce quickly. Selection of new models will, of course, involve full consultation with the specialist community, and great care will be taken to ensure consistency with other standards and conventions, such as those of the International Earth Rotation Service.

An important feature of the SOFA software will be the accompanying documentation. This will include test examples, allowing other implementors of the same algorithms to check for consistency and accuracy, something which is very difficult to do at present.


Fukushima, T. (1995) ``Report of the IAU WGAS Subgroup on Standard Procedures'', in Highlights of Astronomy, vol. 10.

Wallace, P.T. 1996, in Astronomical Data Analysis Software and Systems V, A.S.P. Conf. Ser. Vol. 101, eds. George H. Jacoby and Jeanette Barnes (San Francisco: ASP), 207.

Wallace, P.T. 1997, Starlink User Note 67.

Kaplan, G.H. 1996, Naval Observatory Vector Astrometry Subroutines.