Visual Education (Jan 1923-Dec 1924)

86 Visual Educatio STAR CLUSTER AND BLACK SPOT IN SAGITTARIUS Photographed by E. E. Barnard with the Bruce telesccpe, with an exposure of four and a half hours The Milky Way is a vast aggregation of suns — that is, stars — of large intrinsic brightness. It is probable that most of these stars are considerably larger, hotter and brighter than our sun. At some point the stars are concentrated in such a definite way as to receive the designation of star clouds. The picture shows a black spot, once thought to have been a vacant gap but now believed to be a dark mass of absorbing matter which is projected against the background of stars. The stars which are visible in the black spot are, therefore, nearer to us than the absorbing matter. most valuable kind of work, and as a result of experiments inaugurated with this telescope by Schlesinger, a campaign has been made for finding the distances of the stars with an accuracy far superior to any previous attempt. This has been taken up by other refractors, so that these results are some of the most important contributions to astronomy of the past fifteen years. Study of Nebulae and the Spectroscope Photography, particularly with reflectors, has in recent years brought us a wealth of information concerning the nebulae which have been only partially studied. Several hundred new nebulae have been found on a single plate taken with the twenty-four-inch reflector of the Yerkes Observatory. It is figured that there are millions of them within reach of our present instruments. The intricacies of the great gaseous ones are brought out more clearly on the photograph than could ever be drawn by the human hand, and the wonderful spirals are revealed in a great variety of aspects. We must entirely pass over the whole subject of the application of photography to the use of the spectroscope in astronomy. The camera has been of almost greater benefit to this branch of research than to those described above, and has resulted in our knowledge of the speed of several thousand stars, in miles per second, in the line of sight; in the detection of extraordinary double stars which spin about each other in periods of a few hours, and in the revelation of many other important facts about the sun, the planets, the nebulae, and the stars. The Screen — Everybody's Telescope Our title is "Visualized Astronomy," and it is therefore hardly necessary for us to emphasize further the immense value in education of these applications of photography. Lantern slides and movie films, copied from the original negatives made at observatories, can be exhibited to students and to public audiences with the greatest ease, and actually a far better view is thus obtained of these celestial objects than could be had by the direct use of the most powerful telescopes in existence. In other words, every one may have the opportunity to see any of the celestial objects just as well as the trained astronomer; the entire subject is within the reach of the whole world. Prints and copies on glass are placed at the disposal of other astronomers not having like facilities, who can conduct researches upon them at their leisure and with the most precise of measuring machines, quite as well as though they were equipped with similar telescopes. What has been accomplished in the past thirty years is but a beginning, because of the constant improvement in photographic plates due to the scientific research laboratories conducted by the greatest manufacturers of photographic {Continued on page 94)