National Geographic : 1932 Nov
OBSERVING A TOTAL ECLIPSE OF THE SUN Dimming Solar Light for a Few Seconds Entails Years of Work for Science and Attracts Throngs to "Nature's Most Magnificent Spectacle" BY PAUL A. MCNALLY, S. J., PH. D. Director, Georgetown College Observatory NOT in recent times has an eclipse of the sun awakened a more general public interest than did the total solar eclipse of August 31, 1932. Occur ring during the vacation season and to be seen to best advantage in a famous resort region, it was featured far and wide as an added attraction of the picturesque dis tricts through which it would pass. Few who had passed fifty years of age could hope to see another total solar eclipse in the United States, and the newspapers, es pecially in the East, with their interesting drawings, pictures, and accounts, made the eclipse worth seeing for persons of all ages. Late August found groups from far cor ners of the world making their way to ward the vantage grounds in Canada and New England, fearful, yet hopeful, that some kind disposition of weather would bless the spot they chose, so that they might stand beneath a cloudless sky and enjoy Nature's most magnificent spectacle. Judged from a weather average of more than eleven years, the chances were not very great that anyone would see the to tality. This factor of uncertainty, how ever, instead of quenching, seemed to fan the flame of enthusiasm to greater heights. Suddenly the meeting of Sun and Moon became a great National Occasion and peo ple from all walks of life made ready to join their fellows in doing homage to Na ture's beauteous showing in the sky. What ever the contributing causes, and there were many, the fact remains that the recent total solar eclipse stands quite unique as a phenomenon of Nature awakening an en thusiastic interest in a vast multitude of people. CAUSES OF THE PHENOMENON While the causes of the popular enthu siasm may be difficult to determine, the causes of the phenomenon itself can read ily be understood. When a dark object is brought into the neighborhood of a source of light, it will cast a shadow, and if there be a surface of some sort properly placed to catch the shadow, the size and shape of the shadow can be studied. This is exactly what we have in the solar system. The sun is the earth's great source of light, and the planets and their satellites are all dark objects casting shadows in the direction away from the sun. As the mem bers of the solar system are all approxi mately spherical in shape, the shadows cast are long cones stretching through space along the line joining the center of the sun and the center of the planet or satellite. ECLIPSES VARY IN TIME, PLACE, AND DURATION Were it possible to visit at will the neigh borhood of the various members of the solar system, the spectacle of an eclipse could be seen again and again, as each planet and satellite is constantly casting its long conical shadow out through space. That we do not see these shadows is due entirely to the fact that in most cases there is no surface on which they are cast. The earth is in such a position that it comes, at fairly regular intervals, into the shadow cast by the moon, and then we have a solar eclipse (see, also, page 596). It is clear, then, that the first necessary element for a solar eclipse on the earth is that the three bodies-sun, moon, and earth-should be in the same straight line. However, this condition is sometimes pres ent and yet no total eclipse is seen, because, the moon at the time being too far from the earth, the long shadow cone does not quite reach the earth and the edges of the sun can be seen all around the moon. This kind of eclipse is called annular or ring shaped. Relative to the earth, the shadow of the moon where it touches the earth is small. averaging about 80 miles in width; so that the portion of the earth from which a par ticular eclipse may be seen is restricted.