Fine structure of the celestial polarization pattern and its temporal change during the total solar eclipse of 11 August 1999

Using 180° field-of-view (full-sky) imaging polarimetry, we measured the spatiotemporal change of the polarization pattern of the entire celestial hemisphere during the total solar eclipse of 11 August 1999 in Kecel, Hungary. We compared these patterns with the normal celestial polarization patterns measured at the same times on the subsequent day of the eclipse. As a second control sky, the celestial polarization pattern measured on 26 August 1999 in Tunisia was chosen with the same solar zenith distance as that at the Hungarian eclipse. We computed the corresponding theoretical celestial polarization patterns on the basis of the single-scattering Rayleigh model. The spectral characteristics of the polarization pattern in the sky during totality were also measured in the red (650 nm), green (550 nm), and blue (450 nm) ranges of the spectrum. A qualitative explanation was given for the origin of the angle of polarization (E-vector) pattern and the neutral point of skylight polarization near the zenith observed during totality. The relation of our results to earlier observations on skylight polarization during total eclipses was analyzed. The agreements with previous eclipse observations were discussed. The reasons for some disagreements with previous eclipse observations were explained in connection with the spectral dependence of skylight polarization and the fine structure of the celestial E-vector pattern during totality.