Solar Sunspot RegionsFor many years solar observatories have been tracking sunspot regions as they move across the solar disk. Daily measurements are made of the sunspot group positions, magnetic classification, maximum magnetic field strength, group number, Zurich class, Penumbra class, compactness class, number of spots, longitudinal extend in degrees, total spot areas, individual spot areas, etc. Greenwich Heliophysical Observatory began a routine monitoring progam in 1874 and continued until 1976, followed by the Debrecen Heliophysical Observatory program.
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