F-region effects of solar eclipse at sunrise, September 1 , 1951

The annular eclipse of September 1, 1951 started before ground surmise along the east coast of the United States but did not reach maximum phase until later. Three high-speed ionospheric stations were operated by the D.T.M., C.I.W. for the eclipse observations. Locations at Charlottesville, Virginia, Derwood, Maryland, and Chincoteague, Virginia established a west-to-east chain with local time difference of approximately twelve minutes. The maximum phase of eclipse occurred at a time (twenty to thirty minutes after ground sunrise) when normal rate of production of ionization (established by control observations) was very high. The results show absence of any ion production at any station for a period of approximately one-half hour centered on time of eclipse maximum. From the moment when two-thirds of the sun was covered, through the maximum phase ( per cent), and until one-third of the sun was uncovered, no ionization was generated. Several possible explanations are discussed: (1) Emitting sources near center of sun\´s disc; (2) Uniform solar emission, but an effective limb darkening; (3) An atmosphere on the moon.