Astronomy: 1905 Solar Eclipse

ASTRONOMY: 1905 SOLAR ECLIPSE

Photography and Eclipse Observations

Since the middle of the nineteenth century solar eclipses had attracted intense interest among astronomers. The invention of photography and its application to astronomical observations made it possible to record with great precision the solar phenomena that eclipses revealed. Although some primitive daguerreotype photographs had been made of both the sun and the moon in the 1840s, the crucial break-through came with Englishman Warren de la Rue's invention of the photoheliograph, a photographic telescope with a fast shutter that could be used to map the surface of the sun.

Solar Prominences

The first significant riddle that astronomical photography resolved concerned the existence of solar prominences, protuberances from the sun's outer edge that had long puzzled astronomers. It was not clear whether they were physical features of the sun or merely optical illusions. De la Rue took his photoheliograph to Spain, which offered the best view of the solar eclipse of 1860, an event that attracted many European astronomers, including Angelo Secchi, the second pioneer of photographic astronomy. Secchi compared his observations with de la Rue's photographs and confirmed that the prominences seen during the eclipse were real.

The Eclipse of 1905

The path of totality of the eclipse again passed through Spain 30 August 1905, which created a scientific tourist attraction for hundreds of astronomers. The United States was represented by three separate teams, two of which were dispatched by the navy. The third, representing the Lick Observatory in California, was headed by the country's leading observational astronomer, William Wallace Campbell. One navy team, with a forty-foot telescopic camera, was stationed in Daroca and included the director of the University of Virginia's McCormick Observatory, Samuel Mitchell. The team included some thirty-five individuals, including the astronomers and their support staff. In his account of the expedition Mitchell described the hard work involved in building sheds to protect the telescopes, in mounting spectroscopes, and establishing a meteorological observatory. On several nights before the eclipse the astronomers had to stay up all night in order to fine-tune their instrumentation.

Results

Since observations must be concentrated in the tiny window of time bracketing the totality of the eclipse, eclipses do not generally produce startling new findings. Rather, they contribute to the slow building of a cumulative data bank that aids in understanding the physical and, through spectroscopy, chemical phenomena observed. (The results of the solar eclipse of 1919 that confirmed the predictions of Einstein's general theory of relativity was a dramatic exception to the rule of slowly gathered cumulative results.) The most fortunate solar astronomers tried to view as many eclipses as they could afford: Campbell witnessed eight solar eclipses between 1898 (India) and 1922 (Australia). Thus the American teams gathered data about the prominences and the solar corona, ultraviolet radiation, polarization phenomena (measured by a photopolarimeter), and the chemical composition of the sun. The 1905 eclipse was significant in the history of American astronomy because of the large number of personnel participating in an international scientific project. More than any other single event, it marked the coming of age of American astronomy.

PEARY AT THE POLE

When Commander Robert Edwin Peary reached the North Pole he knew that, in order to establish that he had accomplished the feat, he would have to make and record accurate observations of his geographical position. These observations he recorded in his log. On 6 April 1909 he wrote: "The Pole at last. The prize of three centuries. My dream and goal for twenty years. Mine at last!" When he wanted to record some geographical observations, however, he found that the sky was overcast, so he pressed on with his instruments and a team of dogs for about ten miles, to a place where the sky had cleared. He took his observations and wrote: "When I had taken my observations, at Camp Jesup in the Western Hemisphere at noon of April 6th, Columbia meridian time, the sun had been in the south. When I had taken my observations at midnight between the 6th and 7th, at the end of my ten-mile march, in the Eastern Hemisphere, the sun was in the South at that point -—but to those at the camp on the other side of the world, only ten miles away, it was in the North." The opposite orientations to the sun proved that he had indeed found the pole.

He then retraced his steps some eight miles toward the pole and on noon of 7 April took another set of observations: "I had now taken thirteen single, or six and a half double, altitudes of the sun, at two different stations, in three different directions, at four different times, and to allow for possible errors in instruments and observations, had traversed in various directions an area of about eight by ten miles across. At some moment during these marches and counter-marches, I had for all practical purposes passed over the point where north and south and east and west blend into one."

Sources:

William Herbert Hobbs, Peary (New York: Macmiiian, 1936);

Robert E. Peary, The North Pole (Washington, D.C.: F. A. Stokes, 1910).

Sources:

Rebecca R. Joslin, Chasing Eclipses: The Total Solar Eclipses of 1905, 1914, 1925 (Boston: Walton, 1925);

Samuel Alfred Mitchell, Eclipses of the Sun (New York: Columbia University Press, 1923).