![]() ![]() The definition of the astronomical unit therefore had to be revised. However, contemporary dynamic astronomy has to be done within the framework of general relativity, and using a coherent system of units and constants. This value was then used to deduce, in SI units (the international system of units) the solar mass parameter, which was thus determined in an indirect manner. However, the precision of modern measurements of distances within the solar system has rendered this procedure pointless.įurthermore, till now, its value in meters was determined experimentally, and so was not only model and observation dependent, but was also a function of the reference system used. The definition used till now was based on a mathematical expression involving the mass of the Sun (MS), the length of the day (D) and a constant k (called Gauss’ constant) whose numerical value was fixed by convention.īased on a Newtonian concept, its original purpose had been to express exactly the relative distances in the solar system, at a time when the distances themselves could not be determined with any precision. It is familiar to professional astronomer, to amateurs and even to the general public as a means of expressing astronomical distances, and in particular those in the solar system. The astronomical unit - au for short - is approximately equal to the distance of the Earth from the Sun. The resolution which redefines the astronomical unit was proposed to the IAU by the IAU working group "Numerical Standards for Fundamental Astronomy" ("Valeurs numériques pour les constantes de l’astronomie fondamentale") in which scientists from the Observatoire de Paris played a major role. ![]()
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