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The Astronomical Unit now
Standish, E. M.
Transits of Venus: New Views of the Solar System and Galaxy, Proceedings of IAU Colloquium #196, held 7-11 June, 2004 in Preston, U.K.. Edited by D.W. Kurtz. Cambridge: Cambridge University Press, p.163-179
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The Astronomical Unit is one of the most basic units of astronomy: the scale of the solar system. Yet its long and colorful history is sprinkled liberally with incorrect descriptions and mis-quoted definitions - today as much as ever. Over the last half century, the accuracy of the au determinations has improved dramatically: optical (triangulation) methods have given way to modern electronic observations, high-speed computers, and dedicated efforts to improve planetary ephemerides. Typical uncertainties in the value of the au have decreased from many tens of thousands of kilometers to the present level of only a few meters. With the solar system providing a very clean, undisturbed dynamical model, the ephemerides have been used for a variety of exotic physical tests: alternative theories of gravitation, d(G)/dt, d(au)/dt, etc. In the beginning of this modern era, the author happened to be a witness to a couple of rather key events; more lately, a participant. A couple of these personal experiences are related.

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