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August 1964.

Oblate Sun? "The most reliable astronomical test for the theory of general relativity is afforded by the motion of Mercury. The perihelion point of its orbit is moving eastward at a faster rate than is predicted from perturbations by other planets. This difference amounts to 43 seconds of arc per century, and is exactly accounted for by Einstein's theory of general relativity.

"R. H. Dicke of Princeton University makes the suggestion that this agreement may be merely a coincidence. If the sun were very slightly oblate, its gravitational field would produce an additional drift of Mercury's perihelion. The sun is generally regarded as spherical, [but] if the sun can be shown to be nonspherical, the chief astronomical evidence for general relativity would be undermined."

Dicke's idea led to many efforts to measure the Sun with extreme accuracy. Astronomers now think that the Sun's polar and equatorial diameters differ by only about 7 milliarcseconds. In this regard, Einstein is vindicated.

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Title Annotation:75, 50 & 25 Years Ago
Author:Sinnott, Roger W.
Publication:Sky & Telescope
Article Type:Brief article
Geographic Code:1USA
Date:Aug 1, 2014
Previous Article:August 1939.
Next Article:August 1989.

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