In anticipation of the forthcoming total eclipse of the sun on June 30, 1954, Lynn Poole explains a schematic model of the planets' orbits around the sun and primitive peoples' reactions to a solar eclipse. He also briefly describes the layers of the earth's atmosphere: troposphere, stratosphere, ionosphere, and exosphere. Film clips from the National Geographic Society document its expedition to Brazil, in conjunction with the Army Air Force, to witness the May 20, 1947 total solar eclipse. Led by Dr. Lyman J. Briggs, the expedition included other notable scientists from institutions around the world, such as Rev. Francis Hayden, Director of the Georgetown University Observatory. Photography of the eclipse, taken by National Geographic's Richard H. Stewart, shows ambient lighting changes and the sun's corona at the height of the eclipse. A drawing and a model show how the moon obscures the light of the sun, and an animated graph shows the radiant heat curve before, during, and after an eclipse.