The proton flare of August 28, 1966

The proton flare of August 28, 1966 began on H records at 15^h21^m35^s UT. It presented an unusually complex development with flare emission occurring in two distinct plages. The brightest part of the flare attained maximum intensity, 152 % of the continuum, between 15^h30^m and 15^h32^m UT. Photometric measurements show that a long-enduring part of the flare continued to decline in intensity until at least 21^h20^m UT.The flare developed first in parts of the plages that were near the extremities of a filament and a complex system of curvilinear absorption structures, possibly an eruptive prominence in projection. During the rise to maximum intensity a large expanding feature moved southward from the site of the flare with a velocity 700 km/sec. Its appearance on monochromatic records of the chromosphere made in the center of H and 0.5 Å on either side was consistent with the effect of an advancing phenomenon that induces a small shift of the H absorption line, first to longer, and then to shorter wavelengths.Two bright flare-filaments were obvious aspects of the event by 15^h28^m and dominated the main phase of the flare. Loop-type prominences were observed in absorption as early as 15^h40^m.This investigation was supported in part by the Office of Naval Research through funds from Nonr-1224(19), and in part by the National Science Foundation through funds from GA-632.