CORONAL PHYSICS FROM ECLIPSE OBSERVATIONS

Solar total eclipses are rare occasions offering the opportunity to make a snapshot of the solar corona. Thanks to the availability of a large radiative flux in the optical region, sophisticated methods can be used from the ground to analyse all parts of the highly structured white-light corona. Coronal absolute intensities and line emissions, including their polarization, are also studied to analyse density and temperature inhomogeneities, velocities and magnetic fields. Detailed density distribution is directly extracted from fine coronal structures. During the July 11, 1991 eclipse, the large 3.6m aperture CFH optical telescope was used to analyse time sequences over small coronal fields and to image the finest structures; results from this experiment are presented with emphasis on small-scale dynamical plasma processes with possible inclusion of wave-phenomena. Finally, to prepare the SOHO mission on coronal physics, we give an overview of what is known on coronal structures from eclipse observations of the past solar cycles: temperatures, densities, velocities, occurence and structure of streamers, coronal holes, threads, overall variability.