PHOTOGRAPHY

The second great engine of astronomical research, that has been added during the past century, is photography. By this means exact maps may be taken of the heavens at any hour of the night, and the precise position of thousands of stars determined with the utmost exactitude. A chart of the heavens, made in this manner, is not only more complete but more accurate than the combined observations of any number of men could possibly be. Moreover, the photographic plate will record the existence of stars which cannot be seen even with the aid of the most powerful telescopes. This is due to the fact that the plate gradually collects light, and its cumulative effect is noticeable, when its immediate effect cannot be perceived. This power of photographic plates is most valuable, and cannot be duplicated in any other manner. We are assured on good authority that “an ordinary good portrait camera with a lens three or four inches in diameter, if properly mounted so that an exposure of several hours can be made, will show stars so minute that they are invisible even in the great Lick telescope.” An international photographic chart of the heavens is now under way, which, when finished, will represent an accurate catalog of every visible sun, star, and planet, in the sky. After this, any unusual body should be quickly discovered.

But photography is employed not only for mapping out the heavens, but for reaching the farthest stars. The moon and the sun have both been photographed repeatedly, and with most instructive results. The first good pictures of the moon were made by Dr. John W. Draper of New York City, in March, 1840. His son, Dr. Henry Draper, succeeded him in this work, and his photographs were considered the best until Rutherfurd began his remarkable work in 1865. After this, much important work was done in the Lick observatory, and elsewhere. The first picture of the sun was taken in 1845, by Fizeau and Foucault, on a daguerreotype plate. Sun spots, total eclipses, etc., are now studied in great detail by this means.