Observing the Second Solar Spectrum at IRSOL

Abstract

The history of the IRSOL observatory is closely related to Second Solar Spectrum observations. Already in 1963 Brueckner observed scattering polarization in the CaI 4227A line. In 1996 the Hanle effect in the quiet chromosphere was measured for the first time in Locarno using the same spectral line. Since 1998 the ZIMPOL system, a polarimeter allowing unprecedented polarimetric precision, has been installed at IRSOL and been constantly upgraded to state-of-the-art technologies thanks to the close collaboration with the Institute of Astronomy in Zurich. It allows to measure the faint signatures of various scattering polarization effects. A brief historical summary of observations related to polarization at IRSOL is given.