Editing Gaussian gravitational constant (section)

====Definition of the astronomical unit====
Gauss intended his constant to be defined using a mean distance<ref group=note>Historically,{{citation needed|date=June 2018}} the term ''mean distance'' was used interchangeably with the elliptical parameter the ''[[semi-major axis]]''. It does not refer to an actual average distance.</ref> of Earth from the Sun of 1 [[astronomical unit]] precisely.<ref name=" Clemence65"/> With the acceptance of the 1964 resolutions, the IAU, in effect, did the opposite: defined the constant as fundamental, and the astronomical unit as derived, the other variables in the definition being already fixed: mass (of the Sun), and time (the day of {{val|86400}} seconds). This transferred the uncertainty from the gravitational constant to uncertainty in the semi-major axis of the Earth-Sun system, which was no longer exactly one au (the au being defined as depending on the value of the gravitational constant).
The astronomical unit thus became a measured quantity rather than a defined, fixed one.<ref name="Herrick65">{{cite journal| last1 = Herrick | first1 = Samuel | title = The fixing of the gaussian gravitational constant and the corresponding geocentric gravitational constant | journal = Proceedings of the IAU Symposium No. 21 | year = 1965| volume = 21 | page = 95|bibcode=1965IAUS...21...95H}}</ref>

In 1976, the IAU reconfirmed the Gaussian constant's status at the XVIth General Assembly in Grenoble,<ref>{{cite web|url=http://www.iau.org/static/resolutions/IAU1976_French.pdf|title=Resolutions of the XVIth General Assembly of the International Astronomical Union, Grenoble, France, 1976}}</ref> declaring it to be a defining constant, and that

{{quote|The astronomical unit of length is that length ({{mvar|A}}) for which the Gaussian gravitational constant ({{mvar|k}}) takes the value {{val|0.01720209895}} when the units of measurement are the astronomical units of length, mass and time. The dimensions of {{math|''k''<sup>2</sup>}} are those of the constant of gravitation ({{mvar|G}}), i.e., {{dimanalysis|length=3|mass=−1|time=−2}}. The term "unit distance" is also used for the length ({{mvar|A}}).}}

From this definition, the mean distance of Earth from the Sun works out to 1.000 000 03 au, but with perturbations by the other planets, which do not average to zero over time, the average distance is 1.000 000 20 au.<ref name=" Clemence65"/>