Evolutionary charts of solar activity (calcium plages) as functions of heliographic longitude and time, 1964-1979

"The richness and diversity of data relating to solar activity present a challenge from the point of view of organization and evaluation. For phenomena such as plages and centers of activity that tend to last for more than one solar rotation, we have found useful a sequence of "evolutionary charts" based on heliographic longitude for successive solar rotations. Such a diagrammatic representation of calcium plages as a function of longitude and time, couples with considerations of heliographic latitude, permits relatively easy and confident recognition of successively returning centers of activity"--Introduction.