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A Novel Technique for Measuring the Solar Radius from Eclipse Light Curves – Results for 2010, 2012, 2013, and 2015

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Abstract

We report on a novel technique for measuring the solar radius during total solar eclipses that exploits light curves recorded just before and after second and third contacts. The measurements are performed by pre-programmed photometers that are deployed over the eclipse paths and are operated without supervision. The recorded light curves are compared to synthetic light curves calculated from high-accuracy ephemerides and lunar-limb profiles constructed from the topographic model of the Moon provided by the Kaguya lunar space mission. A minimization process between the two sets of curves yields the solar radius. Altogether, seventeen determinations have been obtained during the past four total eclipses with the following averages (at a wavelength of 540 nm and scaled to 1 AU): \(959.94\pm0.02~\mbox{arcsec}\) on 11 July 2010, \(960.02\pm0.04~\mbox{arcsec}\) on 13 November 2012, \(959.99\pm0.09~\mbox{arcsec}\) on 3 November 2013, and \(960.01\pm0.09~\mbox{arcsec}\) on 20 March 2015. Part of the differences between these four values may be attributed to weather conditions. Averaging the whole set of measurements yields a radius of \(959.99\pm0.06~\mbox{arcsec}\) (\(696{,}246\pm45~\mbox{km}\)), which agrees excellently well with the most recent data and supports an upward revision of the standard IAU value, as previously suggested.

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Acknowledgements

We are grateful to Gonzague Bosch and Frédéric Bouchar of the TENUM company for their dedicated efforts to build the photometers in a very short time. We express our gratitude to Meleana Adams, Frédérique Arthaud, Charles Azymze, Jean-Pierre Barriot, Cyril Bazin, Brice Boclet, Ludovic Bousquet, Jack Brunet, Paul Castelnau, Isabelle Dhenin, Etienne Dumont, Jean-Christophe Guin, Eric Hervier, Xavier Jubier, Patrick Martinez, Jean-Claude Merlin, Jean Mouette, Alain Perret, Jason Poinot, Julie Prado, Jean-Louis Raynaud, Lydie Sichoix, and Stéphane Thomas for their participation in the deployments of the photometers, to the tour operators \(66^{\circ}\) Nord, Grand Nord Grand Large, Chasseurs d’Eclipses, and to the numerous unknown people who kindly hosted the photometers on their property. We thank Maurizio Emilio very much for providing his software to generate Figure 1. This work was supported by grants from the Centre National d’Etudes Spatiales.

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Authors and Affiliations

  1. Laboratoire d’Astrophysique de Marseille, UMR 7236, CNRS & Aix-Marseille Université, 38 rue Frédéric Joliot-Curie, 13388, Marseille cedex 13, France

    Philippe Lamy & Guillaume Faury

  2. Centre National d’Etudes Spatiales, avenue Edouard Belin, Toulouse, France

    Jean-Yves Prado

  3. AKKA Informatique et Systèmes, 6 rue Roger Camboulives, BP 13633, 31036, Toulouse cedex 1, France

    Olivier Floyd & Guillaume Faury

  4. Institut de Mécanique Céleste et de Calcul des Ephémérides, UMR 8028, CNRS & Observatoire de Paris, 77 avenue Denfert Rochereau, 75014, Paris, France

    Patrick Rocher

  5. Institut d’Astrophysique de Paris, UMR 7095, CNRS & Université Pierre et Marie Curie, 98 Bis Bd Arago, 75014, Paris, France

    Serge Koutchmy

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  1. Philippe Lamy
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  2. Jean-Yves Prado
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Correspondence to Philippe Lamy.

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Lamy, P., Prado, JY., Floyd, O. et al. A Novel Technique for Measuring the Solar Radius from Eclipse Light Curves – Results for 2010, 2012, 2013, and 2015. Sol Phys 290, 2617–2648 (2015). https://doi.org/10.1007/s11207-015-0787-8

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