Today marks the 80th anniversary of the total solar eclipse of October 1, 1940, which was visible in Colombia, Brazil, Venezuela, and South Africa.

One focus of research for this eclipse was its effect upon the ionosphere and radio propagation. As shown from the clipping above (Washington Evening Star, Oct. 1, 1940), scientific teams from the National Geographic Society and Brown University had travelled to Patos, Brazil, and had photographic equipment at the ready. Unfortunately, however, a thick layer of clouds prevented visual study. Other experiments, however, focused on radio propagation and were presumably unaffected by the clouds.

In preparation for the radio studies, the National Bureau of Standards had previously published data regarding normal ionospheric conditions on the date of the eclipse.