Investigations of the auroral luminosity distribution and the dynamics of discrete auroral forms in a historical retrospective

Research results about planetary-scale auroral distributions are presented in a historical retrospective, beginning with the first "maps of isochasms" -- lines of equal visibility of auroras in the firmament -- up to "isoaurora maps" -- lines of equal occurrence frequency of auroras in the zenith. The exploration of auroras in Russia from Lomonosov in the 18th century until the start of the International Geophysical Year (IGY) in 1957 is shortly summed up. We discuss in detail the daytime sector dynamics of individual discrete forms for both quiet conditions and auroral substorms. We present the evolution of conceptions about the succession of discrete auroral forms and their dynamics during disturbance intervals. Visual observations of diffuse auroral forms at midlatitudes suggest that the whole latitudinal interval between the auroral oval and the stable auroral red (SAR) arc is filled up with diffuse luminosity. SAR arcs with intensities of several tens of Rayleigh enclose systematically the region of diffuse luminosity; they are positioned at the border of the plasmasphere.