Eur. Phys. J. H 36, 407-436 (2011)
https://doi.org/10.1140/epjh/e2011-20017-4

History of solar oblateness measurements and interpretation^⋆

¹ Nice University, OCA-LAGRANGE, CNRS UMR 6525, avenue Copernic, 06130 Grasse, France
² INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy

^a e-mail: rozelot@obs-azur.fr
^b e-mail: damiani@oamp.fr

Received: 27 July 2011
Published online: 21 November 2011

Abstract

The story of the solar oblateness begins in the pre-relativity days when an explanation of the observed advance of Mercury’s perihelion was searched for. Then, examination of historical records during the first decade of the twentieth century shows clearly a strong effort to measure the solar shape. Results show discrepancies, due on one hand, to the fact that physical statements in the solar case are still pending (for example does the solar core rotate rapidly? Is the Sun an oblique rotator? How does the magnetic field distort the outer shape?) and on the other hand, due to the difficulty in measuring a faint quantity, even when using the cutting edge of up-to-date techniques. We provide a new perspective on the controversy which followed measurements made in Princeton (USA) in the mid-1960s, highlighting the possibility to advocate alternative theories of gravitation. Since then, the accurate shape of the Sun has been actively debated, and so far, only satellite experiments seem to achieve the required sensitivity to measure the expected faint deviations to sphericity. In a close cooperation between experiments and theory, we point out how false ideas or inexact past measurements may contribute to the advancement of new physical concepts.