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Nouvelle Définition de l'unité astronomique de longueur |
adopted by the XXVIII General Assembly of the IAU (August 2012) adoptée par la XXVIIIè Assemblée générale de l'UAI (Août 2012) (latest update: 27 September 2012) |
The XXVIIIth General Assembly of the International Astronomical Union (IAU) that took place in Beijing, China, from 20 to 31 August 2012, resulted in particular in the re-definition of the astronomical unit of length, which has been adopted as "IAU 2012 Resolution B2". See the IAU News release of 31 August 2012.
Text of the IAU 2012 Resolution B2 (English version)
IAU 2012 Resolution B2: Re-definition of the astronomical unit of length (PDF file: Draft)
Texte de la Résolution B2 (Version française)
Resolution UAI 2012 B2: Re-définition de l’unité astronomique de longueur (PDF file: Version préliminaire)
On the adoption of the new definition by the IAU
Details on the reasons, consequences and process can be found in the document "The re-defintion of the au".
Basis of the Resolution
Details on the IAU Resolution proposal can be found in:
- the paper "Proposal for the re-definition of the astronomical unit of length through a fixed relation to the SI meter" (Capitaine, Guinot, Klioner, 2011), published in the Proceedings of the Journées 2010 "Systèmes de Référence Spatio-Temporels", and/or the corresponding PPT Presentation (PDF file)
- a press release on the proposal (27 May 2012) along with a more detailed technical information document (10 June 2012)
- a few slides providing a summary of the New Definition of the Astronomical Unit (PDF file) by Capitaine, Klioner, McCarthy (12 June 2012)
The old definition of the astronomical unit
That length for which the Gaussian gravitational constant (k) takes the value of 0.01720209895 when the units of measurements are the astronomical unit of length, mass and time. The dimensions of k2 are those of the constant of gravitation (G), i.e., L3M-1T-2.
(Equivalently, the radius of an unperturbed circular Newtonian orbit about the Sun of a particle having infinitesimal mass, moving with an angular frequency of 0.017 202 098 95 radians per day.)
The new definition of the astronomical unit
A conventional unit of length equal to 149 597 870 700 m exactly. This definition has to be used with all time scales such as TCB, TDB, TCG, TT, etc.
The unique symbol to be used for the astronomical unit is “au”.
Previous IAU Resolutions
IAU 2000 Resolutions on reference systems
IAU Resolutions adopted at the General Assemblies (1922-2012)