Astronomy for Everybody/Part 2/Chapter 3

One of the greatest advances in practical astronomy in our time has been brought about by photographing the heavenly bodies. This is so simple a process that the slowness of its introduction may seem curious. Back in the early '40's, Professor Draper, of New York, the well-known chemist, succeeded in making a daguerreotype of the moon. When the system of photography by our present process on a glass negative was invented, Professor Bond, of the Harvard Observatory, and Mr. L. M. Rutherford, an eminent astronomer of New York, both began to apply the art to the moon and stars. Mr. Rutherford brought his work to such perfection that his photographs of the Pleiades and other clusters of stars are still of great value in astronomy.

A photograph of the stars can be made by an ordinary camera if we only mount it like an equatorial telescope so that it shall follow the star in its diurnal motion. A very few minutes exposure will suffice to take a picture of more stars than can be seen by the naked eye; in fact, with a large camera, this will not require a minute. But what is generally used by the astronomer is a photographic telescope. Any ordinary telescope will serve the purpose, but in order to get the best results the object-glass of the telescope must be especially made to ​bring to a focus those rays of light to which the photographic film is most sensitive. So rapid has been the progress during the past few years that the greater part of the astronomical work of the future seems likely to be done by photography. The great advantage of the method is that when a picture either of some heavenly body or of the stars in the sky is taken, it can be studied and measured at leisure with all the care the astronomer chooses to bestow upon it, while the observation in the heavens is nearly always more or less hurried, and made difficult by the diurnal motion of the star.

Formerly the spots on the sun were investigated by watching that luminary through the telescope, recording the number of spots, and measuring their position on the solar disk. Now, at the Greenwich Observatory and elsewhere, a photograph of the sun is taken almost every day, and the position of the spots is found by measuring the photograph. Thus a study of the sun and the changes going on on its surface is kept up from year to year.

Formerly the astronomer studied the physical constitution of a comet by making a drawing of it. This was a rather uncertain process, and as a general rule no two men would quite agree in the minute details. Now the comet is photographed and a study is made upon the negative. The same remark applies to nebulae. Drawings of them are no longer made—only photographs which show a great deal more than any drawing will.