The solar flares of August 28 and 30, 1966

We describe observations of the class 3+ flare of August 28, 1966, made at the Mount Wilson Observatory. This great proton flare followed the sequence: (1) Precursor flare; (2) Filament eruption; (3) Beginning in penumbra of large spot; (4) Rapid elongation in two strands; (5) Great spray and surface wave; (6) Rapid separation of two strands to maximum brightness; and (7) Slow spread of brightness and decay.The soft X-ray burst coincides with stages 3–6, decaying through stage 7; the hard (> 80 keV) burst coincides, but decays more rapidly.Considering a demi-cylinder of emitting material, the soft X-rays are explained by a 4-million-degree plasma, or at least a large flux of electrons with that amount of energy. Given this flux, the microwave burst is explained by synchrotron emission with the low frequency cut-off due to coronal absorption.The class-2 flare of August 30, 1966, is also discussed.This research was supported by the Advanced Research Projects Agency under the Office of Naval Research Grant N00014-67-C-0140 and the National Aeronautics and Space Administration under Grant NGR 05 002 034.NASA International University Fellow at the California Institute of Technology, 1967–1968, now at Arcetri Astrophysical Observatory.