National Geographic : 1937 Feb
OBSERVING AN ECLIPSE IN ASIATIC RUSSIA BY IRVINE C. GARDNER Leader of the National Geographic Society-National Bureau of Standards Eclipse Expedition UNDER the sponsorship of the Na tional Geographic Society and the National Bureau of Standards, it was my good fortune to observe in Asiatic Russia the solar eclipse of June 19, 1936. Excellent weather conditions permitted the making of satisfactory photographs of the solar corona in black and white and also in color. This successful outcome enables THE NATIONAL GEOGRAPHIC MAGAZINE to reproduce the first natural-color photo graph of a total eclipse ever published (op posite page). Observation of a total solar eclipse is one of the most thrilling gambles of sci entific research. After elaborate and highly specialized apparatus has been built, taken possibly a third or halfway around the world, and set up with meticulous care, the best that can be hoped for usually is two or three minutes of observing time. Even that outcome is entirely dependent upon the caprice of the weather. A tiny cloud over the sun may spoil everything. Dame Nature must have been in a truly sporting mood when she provided the eclipse-producing mechanism for the earth. ECLIPSES FREQUENT ON JUPITER She did much better for Jupiter. Jupi terians, if there were such people, would be well supplied with solar eclipses by the sev eral moons large enough to produce them frequently. In fact, it is not unusual for two or three total solar eclipses to be pro ceeding on Jupiter at the same time. From the earth, with a telescope of moderate size, one may see the black, ap proximately circular shadows of the satel lites as they travel across the disk of Jupi ter. These shadows represent regions of total eclipse on that planet. The earth, however, has only one moon. Its orbit and size are such that it appears slightly smaller than the sun when it is most remote from the earth and a little larger in its nearer positions. Its path comes di rectly between the earth and the sun only at rare intervals. Then, if it is sufficiently near the earth to blot out the sun entirely, its elliptical shadow lying on the earth is the area within which the sun is totally eclipsed. As a result of the rotation of the earth and the apparent motions of the sun and moon, this elliptical shadow sweeps over a long, narrow strip extending approximately a third of the way around the earth. Only along that path is a total solar eclipse visible. Eclipses seem to have a predilection for visiting inaccessible places. The coming eclipse of June 8, 1937, for example, will have a maximum duration of seven minutes and four seconds, an extraordinarily long period, but the region from which it can be viewed lies almost entirely in the Pacific Ocean and there are only a few small islands which afford sites for eclipse ex peditions.* The eclipse of 1936 was much more ac commodating. It was total over a narrow shaded strip beginning in the Mediter ranean south of Italy, crossing Greece and Soviet Russia, and ending in Japan. In central and eastern Siberia, the only terri tory conveniently accessible was that along the Trans-Siberian Railroad; indeed, the central line of this eclipse path followed the railroad so closely as to cross it five times. An early problem of an eclipse expedi tion is the selection of a site. Near the middle of this strip of territory the eclipse would be at noon, an advantage because of the height of the sun at that hour and the consequent increased dura tion of the eclipse. The probabilities of fair weather, however, had also to be taken into consideration. SITE STUDIED TWO YEARS IN ADVANCE The U. S. S. R. Government generously authorized a study of the advantages and disadvantages of different possible loca tions for eclipse expeditions. This study was made two years in advance of the eclipse, and the results were published in English by Dr. B. P. Gerasimovic and Dr. H. J. Scerbakova, and by Dr. A. Michailov. These publications enabled foreign astrono mers to compare the advantages and dis advantages of different parts of the total eclipse region lying within Russia. Taken into consideration were the prob ability of a clear sky, temperature, freedom from dust storms, freedom from strong winds which might shake the instruments, * See "The Society's New Map of the Pacific," by Gilbert Grosvenor, NATIONAL GEOGRAPHIC MAGAZINE, December, 1936.