Photometrie photographique de la couronne solaire

Abstract

A series of plates of the solar corona were obtained during the total solar eclipse of July 10th, 1972 near Anadyr (U.S.S.R.) using a standard eclipse coronagraph of Ø = 20 cm and F = 300 cm. A neutral radial filter (Figure 2) was specially conceived to enable the study of the corona up to 5 R _⊙ and also that of the lunar background. The absolute calibration takes into consideration the different components of the recorded radiation: the K and F corona, the sky background B _c, the coronal aureola B _aur and details of the earthshine on the lunar background. The brightness of the corona (K + F) is given along the N-S and E-W axes and also the total brightness recorded along the tangential directions, at selected radial distances.

The photometry shows that the K corona in 1972 was very heterogeneous and its mean brightness close to that of a corona of maximum activity for r < 2 R _⊙. Moreover, the difference of brightness between the equator and the poles for r > 2 R _bd is about twice larger than in the Van de Hulst' model of the corona of minimum activity. At the north pole, a coronal ‘hole’ clearly appears.