Detailed Study of the Development of an Active Solar Region, 1954 August 20-27

The week of 1954 August 20–27 provided an opportunity to study the development of an active solar region under circumstances of unusual simplicity. The calcium plage formed near the central meridian of the solar disk between $${15}^\text{h}{00}^\text{m}\,\text{and}\,{15}^\text{h}{10}^\text{m}$$ U.T. on August 20. In the week following its formation, the calcium plage grew to at least 3500 millionths of the solar hemisphere and became 2·4 times as bright as the dark portions of the mottled background of the K₂₃₂ spectroheliograms. Isophotometric studies of the calcium plage provide quantitative data for comparison with sunspot, magnetic, geomagnetic, radio flux, and coronal data made available by astronomers in all parts of the world. At least five flares or subflares were observed in the region before it traversed the west limb. The study presents a comprehensive and partially quantitative account of of the formation, growth and decline of an isolated centre of solar activity. The problems encountered are illustrative of those that will be met on a grander scale in the solar studies of the International Geophysical Year.