National Geographic : 1947 May
Your Society Observes Eclipse in Brazil ON MAY 20, 1947, from a camp in the Behavior of the ionosphere, the radio high rolling country of the interior of reflecting layer high above the earth, will be southern Brazil, an expedition of the studied during the eclipse. The ionosphere is National Geographic Society will observe for composed of several layers of air which are the seventh time a total eclipse of the sun. ionized, or made electrically conducting, by This expedition is a joint undertaking of ultraviolet light and particles from the sun. your Society and the United States Army Air Using radio impulses as probing tools to Forces and is already established near the reach up from 50 to 250 miles aloft, the scien village of Bocaiuva, 400 miles north of Rio tists will investigate what happens to the iono de Janeiro. The site was chosen because it sphere when these radiations from the sun are offers the best likelihood of clear skies at cut off during the eclipse. eclipse time. Terrifically hot gases of the sun's chromo Dr. Lyman J. Briggs, Chairman of your sphere, just above its surface, and the corona, Society's Research Committee, will lead a the thin, nebulous envelope of gas surrounding group of 14 scientists from the National Bu- the sun far out in space, will be investigated reau of Standards, Yerkes Observatory, Lick with spectrographs. These instruments break Observatory, Georgetown University Observa- up light into its various wave lengths, which tory, Bartol Research Foundation, U. S. reveal what elements are present in these gases Naval Research Laboratory, and Army Air and how they are affected by the sun's intense Forces. heat. Photographs of the eclipse from a B-17 A Much-traveled Camera bomber flying at 30,000 feet will be taken by The sun's corona will be photographed in Army Air Forces photographers. They also black and white and in color with a much will attempt to photograph the moon's shadow traveled camera which previously has photo as it races across the ground below. graphed eclipses in Brazil, Russia, and on First Television of Eclipse Canton Island in the Pacific.* This eclipse will be the first in history to be Measurements of the exact times of the four televised. Motion pictures of the eclipse will "contacts," the times when the moon begins to be flown immediately to the United States cover the sun, when it completely covers it, and sent out over television channels within when the sun begins to emerge from behind 48 hours after the event, the moon, and when the sun completely In addition, the eclipse will be described as emerges, will be carried out. it takes place in a special broadcast by short- These will provide a check on the move wave radio. The eclipse will not be visible in ments of the sun, moon, and earth in relation the United States. to one another and to the stars, upon which The period of totality will be 3 minutes and are based our measurements of time. 48 seconds at Bocaiuva, from 9:34.8 to 9:38.6 An elaborate program of meteorological ob a. m. local time. This will correspond to 7:34.8 servations, before, during, and after the eclipse, to 7:38.6 a. m. Eastern Standard Time, since to help determine whether it has any effect on eastern Brazil is in the second time zone east the weather, will be carried out by the Army of New York. Air Forces. An important feature of the expedition's These data also will be used in the calcula program will be a check on the validity of tions of the bending of starlight in the rela the Einstein theory of relativity, with its tivity experiment. strange concepts that space is curved and that Whether or not the eclipse has any effect on everything has a fourth dimension-time. the mysterious cosmic rays that fall continu This check will be made by photographing ally upon the earth from outer space will be certain stars that will be visible near the sun investigated. Observations to determine how during the eclipse. If the Einstein theory is the intensity of cosmic rays varies with lati correct, the light rays coming from these stars tude and altitude also will be made. will be slightly bent by the gravitational pull * See, in the NATIONAL GEOGRAPHIC MAGAZINE: of te sun as they pass by it. This will cause "Observing a Total Eclipse of the Sun," by Paul A. of the sun as they pass by it. This wil cause McNally, November, 1932; "Photographing the the star images on the photographic plates to Eclipse of 1932 from the Air," by Capt. Albert W. be slightly displaced from their actual posi- Stevens, November, 1932; "Eclipse Adventures on a tions. Desert Isle (Canton)," by Capt. J. F. Hellweg, Sep Comparing these pictures with others taken tember, 1937; "Nature's Most Dramatic Spectacle," of the same stars six months later will reveal by S. A. Mitchell, September, 1937; and "Observing of the same stars six months later will reveal an Eclipse in Asiatic Russia," by Irvine C. Gardner, whether this bending took place. February, 1937.