Article

# "IMPRINTING" IN GENERAL RELATIVITY TESTS?

International Journal of Modern Physics D (Impact Factor: 1.03). 09/2011; 20(10):1945-1948. DOI:10.1142/S0218271811019980
Source: arXiv

ABSTRACT We investigate possible a priori "imprinting" of general relativity itself on spaceraft-based tests of it. We deal with some performed or proposed time-delay ranging experiments in the Sun's gravitational field. The "imprint" of general relativity on the Astronomical Unit and the solar gravitational constant GM⊙, not solved for in the spacecraft-based time-delay test performed so far, may induce an a priori bias of the order of 10-6 in typical solar system ranging experiments aimed to measuring the space curvature PPN parameter γ. It is too small by one order of magnitude to be of concern for the performed Cassini experiment, but it would affect future planned or proposed tests aiming to reach a 10-7–10-9 accuracy in determining γ.

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##### Article: The Astronomical Unit now
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ABSTRACT: 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, $d({\rm G})/dt$, $d({\rm au})/dt$, 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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