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

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.