Deeper Into Space: The New Telescope and Our Universe

I

FIVE years ago the Rockefeller Trustees, with the approval and support of John D. Rockefeller, Jr., made provision for two far-reaching explorations. One of these, organized by my old friend Breasted, involves the most comprehensive study ever undertaken of the origin and rise of civilization in the Near East. This combines the excavation, recording, and interpretation of ancient remains and inscriptions at numerous carefully chosen stations in Egypt and the Near East with a geological survey of the Nile Valley, linking the partially known historic period to the remote prehistoric era. Thus Breasted is creating a unified picture of human progress in the most strategic region of the world, with a sweeping vision reaching back over hundreds of thousands of years into the dim and distant epoch of the past.

The other grant made by the Rockefeller Trustees was for an investigation complementary to that of Breasted and his associates. Sixty centuries ago, on the banks of the Nile, the pioneer astronomers of Egypt watched the meridian passage of the stars and mapped the principal constellations. Hundreds of Babylonian tablets also preserve astronomical records, which were continued for centuries and led to the capital discovery of the precession of the equinoxes. In those early days the great distance of the stars was unknown, but, as the centuries rolled by, the heavens seemed to recede from the earth. Increased precision of observation showed the stars to be very remote, and enhanced the desire for greater knowledge. The speculations and observations of the early Greeks and the persistent work of the Alexandrian School added largely to the already vast literature of astronomy. Even the decline of Alexandria and the ignorance of the Dark Ages did not long hamper progress, as the books of the Greeks were preserved and their observations continued in all parts of the Arabian empire. Astronomy thus spread through Moorish Spain to other parts of Europe, and in the century of Copernicus the most elaborate observatory of the period was established by Tycho Brahe on a Danish island. Here were obtained the positions of the planets from which Kepler derived their laws of motion, which finally led to the great generalization of Newton. At the end of the seventeenth century the only known stars were the small number visible to the naked eye. Then came Galileo’s telescope. Suddenly tens of thousands of hitherto unseen stars burst into view, and with them the mountains on the Moon, the satellites of Jupiter, and the phases of Venus. Thus the reasoning of Copernicus, who had placed the sun instead of the earth at the centre of the solar system, was finally confirmed. The telescope continued to grow, recently attaining a diameter of one hundred inches and revealing thousands of millions of stars. During the last century its efficiency has been greatly enhanced by combining with it such chemical and physical devices as the photographic plate, the spectroscope, and the photoelectric amplifier.

My own experience, covering a period of fifty years, has led me to realize the importance of a broad and constantly developing research policy. I do not believe in hastily casting aside the methods and experience of the past, but rather in utilizing and improving them in harmony with the steady advance of science. As a boy I made the most of my own apparatus, and experimented in chemistry and physics before I entered astronomy. My first spectroscope was in use before I built my first, telescope, and a small camera preceded them both. Thus it was natural to combine all three, as Huggins and others had done, and to give sufficient space in my first observatory to a laboratory and workshop. Such a policy, continued at the Yerkes and Mount Wilson Observatories, is also the fundamental principle of the new project described in these pages.

Another prime element in this policy is that of coöperation in research. Research laboratories and observatories should not be organized as competing institutions, largely intent on their own glory. On the other hand, a group of observatories should not be conducted as unthinking machines, operated by a single head. Whenever possible, plans of cooperation should be devised, in which all of the originality of each individual investigator is stimulated and encouraged without sacrifice of the great advantages of joint operation and control. I could give numerous examples of local, national, and international coöperation in research which have proved extremely fruitful.

The most richly endowed research agencies in the United States are those directed by the Rockefeller and the Carnegie Trustees. While these bodies differ in certain respects in organization and procedure, their purposes have much in common. Thus in 1903 the Carnegie Institution of Washington established a large observatory on Mount Wilson and in Pasadena, and later it greatly aided in the development of the California Institute of Technology, also in Pasadena. The Rockefeller Boards showed a special interest in the California Institute, to which, with their assistance, such outstanding leaders of research as Arthur A. Noyes, Robert A. Millikan, and Thomas Hunt Morgan were drawn.

In 1928 the Rockefeller Trustees offered to the California Institute a sum sufficient to build a 200-inch reflecting telescope, together with such instrument shops, laboratories, and other facilities as would be required to establish a well-rounded Astrophysical Observatory. This Observatory was designed to be complementary to the Mount Wilson Observatory, and in no sense a rival institution. A necessary condition of the gift was therefore that the Carnegie Institution of Washington should coöperate in the most complete way with the California Institute. Such coöperation was cordially promised by the President and the Executive Committee of the Carnegie Institution. Reciprocally, the California Institute offered the use of its facilities to members of the staff of the Mount Wilson Observatory. The Institute’s Physical and Chemical Laboratories, not to speak of the possibilities of its new astrophysical equipment, will thus be available for researches in which they may be needed by the Mount Wilson observers.

II

The reader may inquire why, when so many stars are known, we need an instrument large enough to add hundreds of millions more. The answer is easy to give. The discovery of stars previously unknown because of their faintness is important only in so far as they may contribute to our knowledge of the structure of the universe and the nature of its constituents. Until recently all of the heavenly bodies have generally been looked upon as parts of a single Galaxy, a flattened aggregation with its greatest extension in the plane of the Milky Way. The first nebula recognized to have a spiral form was detected by Lord Rosse’s great reflecting telescope in 1845, but a few years ago strong arguments were advanced for the belief that the hundreds of thousands of spiral nebulæ then known were members of our own Galaxy.

Other astronomers, however, already held opposite views. Indeed, the conception of ‘island universes,’ scattered through the depths of space, goes back more than a century. But speculation is a very different thing from proof. Gradually, by the aid of powerful telescopes equipped with photographic and spectroscopic appliances, the distance of the spiral nebulæ has been measured, and they are now generally regarded to be outside our galactic system, most of them at enormous distances. We have also learned that the Galaxy, with its hundreds of millions of stars, is probably itself a spiral nebula, whirling with the astonishing velocity that characterizes these objects. Long-exposure photographs of the nearest spirals have partially resolved them into extremely faint stars, and afforded means of comparing them with similar stars in our own system and thus of measuring their distance. Finally, the millions of ‘island universes’ (many of them spiral nebulæ) scattered through space appear to be separating at velocities which are almost comparable with the velocity of light. But there are some apparent contradictions in this picture, which can be investigated only by the aid of a telescope capable of reaching farther into space.

This, however, is only one side of the problem of modern astrophysics. We have learned that t he earth is one of the smallest members of a group of planets revolving about the sun, and that the sun, far removed from the centre of the Galaxy, is one of the smallest stars. The study of the structure and evolution of the stars began about the time of Darwin’s publication of The On gin of Species. Indeed, the first chemical analysis of the sun was made by Kirchhoff and Bunsen in that same memorable year — 1859. Similar analyses of the brighter stars, conducted within a decade by Huggins and Secchi, showed the presence of the same elements found in the earth and sun. They also revealed a distinct sequence among the stars, pointing toward a definite law of evolution. As time went on, it also appeared that we must look to the stars for the solution of some of the most fundamental questions of chemistry and physics.

Thus the true rôle of astrophysics is a very broad one. It shows us a vast universe, aglow with near and distant objects which appeal to us in a double sense. To the celestial problem, which the work of many centuries has shown to be one of the earliest and most persistent interests of mankind, is added a great terrestrial asset. For we now realize that the heavens contain innumerable stellar laboratories, where problems of physics and chemistry, far beyond the capacity of our laboratories on earth, are open to solution.

When Einstein conceived his theory, and stimulated its test by means of the sun and stars, no physicist could have shown in the laboratory that the passage of light rays near a mass of matter would result in the bending of their path. Nor, without the aid of a huge gaseous body like the sun, could the physicist have proved that the radiation of luminous atoms is altered by the neighborhood of such a mass. Scores of illustrations might be given to indicate the value of ‘ cosmic crucibles’ in solving laboratory problems. As astronomy is dependent, in still greater degree, upon the fundamental sciences of physics and chemistry, it is perfectly clear that all three should be cultivated together, with the indispensable aid of mathematics.

In this extensive unified work a telescope much more powerful than any yet available is urgently needed. It is not a question, as is so commonly supposed, of great magnifying power. What we must have is more light, focused in a sharply defined image. To get more light it is necessary to enlarge the curved optical surface used to concentrate all the rays falling upon it. The problems involved in constructing and operating a greater telescope are easy to name but difficult to solve.

The first necessity is to make disks of glass or some other suitable material of sufficient size, stiffness, homogeneity, and freedom from marked distortion by change of temperature.

The next is to give such a disk a practically perfect optical surface and to coat its curved face uniformly with a highly reflecting film of silver or other suitable metal.

While this process, involving many years of work, is under way, a telescope mounting must be designed and built. This must be capable of supporting the massive optical disk so perfectly that it will be undistorted in any position. It must also automatically follow the stars with great precision throughout the night.

At the same time a careful comparative study must be made of promising sites for the telescope, in a region where much clear weather and other favorable conditions prevail. The long construction period will also give opportunity for other work of equal importance, including the erection of shops and laboratories and the design and construction of auxiliary apparatus capable of multiplying many fold the efficiency of the telescope.

Throughout the centuries separating Galileo from the earliest astronomers, the only collector of starlight available was the unaided eye. The huge astronomical instruments erected in Cairo, India, Denmark, and elsewhere revealed no stars beyond the range of ordinary vision; they served merely to determine the positions and motions of the visible stars and planets. Although lenses had been used earlier as aids to vision, Galileo was the first to apply them to the heavens. His telescope, with its simple convex lens about two and one-quarter inches in diameter, collected about eighty times as much light as the pupil of the eye. This gain was sufficient to add hundreds of thousands of stars to the two or three thousand previously seen. Now it is a question, not so much of multiplying the hundreds of millions of stars already known, as of brightening their images and of making possible a satisfactory exploration of the vast world of distant galaxies lying beyond the limits of the Milky Way.

III

After years of ingenious experimentation by the General Electric Company with fused quartz, which offers hitherto insuperable difficulties in very large masses because of its extremely high melting point, we turned to Pyrex glass, so widely known because of its superiority to ordinary glass for cooking purposes. Its high quartz content greatly reduces its expansion by heat, and explains why Pyrex utensils withstand without cracking the sudden changes of temperature to which they are often exposed. The casting and annealing of large Pyrex disks demanded, however, extensive studies by experienced physicists, and we were very fortunate to be able to call upon the knowledge and experience of Dr. Arthur L. Day, Director of the Geophysical Laboratory of the Carnegie Institution of Washington, and the able research staff of the Corning Glass Works.

After a 60-inch Pyrex disk had been successfully made, a glass much superior for our purposes to ordinary Pyrex was developed for us, and used to make the 72-inch disk for the telescope of the new Toronto Observatory. A 120-inch disk (needed for testing the 200-inch mirror) was then cast for us last June. It was carefully annealed by a special process, and when taken from the annealing furnace in December it was shown by preliminary tests to be of the highest quality. On the last day of the year, an 80-inch disk, for the new observatory of the University of Texas, was cast at Corning from the same kind of glass. Thus the Rockefeller gift to the California Institute, as will be shown more fully later, is accomplishing the purpose of developing new methods and materials needed by many institutions, instead of being solely devoted to the establishment of a single new observatory.

A 120-inch disk having been cast, with an area half again as great as that of the largest telescope mirror previously made, we may look forward with confidence to the success of the 200-inch disk. This will be cast within a few weeks (shortly after the casting of a 60-inch disk for the Harvard College Observatory), and its annealing should be completed by the end of 1934. Then follows the long and delicate process of grinding, polishing, and figuring the disk after its arrival in Pasadena.

At this point a word should be said regarding the preparations already made at the California Institute. The first need was a suitable machine shop, equipped with the tools required to build the special instruments, of many new types, called for in this enterprise. Here, too, a large grinding and polishing machine has been designed and built. This machine is nearly ready for work on the 120-inch disk in our new optical shop, completed a few months ago. No such building is available elsewhere, because of the large scale and the special requirements of the task. It must not only permit the 120-inch and 200-inch disks to be ground, polished, and figured to the highest perfection, but also to be tested optically in combination with each other. These operations demand a room 54 feet wide, 162 feet long, and 39 feet high, in which the dust-free air can be maintained for many months at nearly constant temperature and humidity. Overhead an electric crane, tested for loads of fifty tons, spans the room and travels its entire length. By this means the heavy disks can be lifted on or off the polishing machines and moved about at will. Small optical shops adjoin the main room and afford space for all the minor work.

When finally completed, the 200-ineh mirror will have a polished concave face, not differing from a true paraboloidal form by more than two millionths of an inch.

The ordinary method of coating such a telescope mirror is to deposit on it chemically a very thin layer of pure silver. Four years ago, however, John Strong developed at the University of Michigan a process of vaporizing various metals, and depositing the vapor on glass or any other substance in a high vacuum. Now a member of the research staff of the California Institute, Strong has recently coated with aluminum mirrors up to thirtysix inches in diameter (the Crossley Reflector of the Lick Observatory), besides many smaller mirrors and gratings used on Mount Wilson and in Pasadena. The remarkable permanence of such aluminum surfaces and their great superiority to silver, especially in the violet and ultra-violet, lead us to hope that this process can be used for coating the 200-inch mirror.

Photographic exposures of faint celestial objects often last for hours, or even for several successive nights. During this time the stars must be kept accurately in position on the plate, in spite of their apparent westward motion caused by the rotation of the earth. The 200-inch mirror, weighing nearly twenty-five tons, must therefore lie on a special support system (to prevent distortion) at the bottom of a steel skeleton tube hung on trunnions between the arms of a huge polar axis, kept in steady rotation by a driving clock and worm gear. The skeleton tube, about twenty-five feet in diameter and sixty feet long, will be so rigid that the observer can be carried at its upper end, within a small cartridge-shaped house at the centre of the tube. The parallel rays of light from the stars, entering the open end of the tube unimpeded except by the central observer’s house and its four narrow supporting steel webs, will fall on the concave mirror at the lower end of the tube and be reflected back to form images which can be observed visually, photographed, analyzed with a spectroscope, or measured with such an instrument as a photoelectric amplifier. The loss of the light obstructed by the observer’s house is unimportant, because it is so small a fraction of the whole light received and also because the central part of the mirror must be covered in any reflecting telescope.

IV

An exceptional feature of the 200inch telescope will be its great angular aperture. In most reflectors the focal length is five or six times the diameter of the large mirror. The focal length of the 200-inch will be only 3.3 times its aperture. Thus the photographic intensity of a given star at its focus will not be merely four times that of the same star at the focus of the 100-inch telescope, but more nearly ten times as great. This means that the 200-inch telescope should penetrate fully three times as far into space, and thus open for investigation an unexplored sphere of about thirty times the volume of that hitherto sounded.

The observations mentioned above are to be made at the primary focus of the 200-inch mirror. In other classes of work different arrangements are called for. A convex mirror about forty inches in diameter, mounted at the centre of the tube below the observer’s house, can be instantly turned into position by an electric motor. This will cause the light rays to converge less rapidly, and form an image of a field of stars on a photographic plate about seventeen inches square just below the 200-inch mirror, which will be pierced with a central hole to transmit the beam. Or the photographic plate holder can be swung aside and replaced by a spectrograph. Because of the varying refraction of the atmosphere, the star images cannot be held precisely in place by the driving clock of the telescope. An observer, carried by the massive tube, must watch a star under considerable magnification and, with the aid of suitable mechanism, make the small corrections necessary to keep it in position at the intersection of two cross hairs or on the slit of the spectrograph.

When longer spectrographs or other auxiliary instruments are needed to analyze the light of stars or nebulæ or to measure their radiation, one or more plane mirrors can be swung into position, displacing the focus to apparatus on either side of the telescope tube or in a fixed constant temperature chamber due south of the polar axis. In this way it will be possible to photograph the spectra of the brighter stars on a scale as great as that ordinarily used in the study of the sun.

The selection of a suitable site for the 200-inch telescope is not an easy problem. Should it be north or south of the equator, and at what latitude? For instruments up to one hundred inches aperture this might prove to be a difficult question, as the southern stars have been explored much less completely than those of the northern sky. But for a 200-inch telescope, which must be devoted exclusively to work beyond the range of smaller instruments, there can be no manner of doubt. The selection of celestial objects for special study cannot be made intelligently without the aid of all the knowledge available. As this is far more abundant for the northern heavens, a site north of the equator is evidently needed. As for its latitude, it is obviously desirable to include as much of the sky as possible, without depressing the north celestial pole too far. A latitude between 30 degrees and 35 degrees, where three fourths of the entire heavens are visible, is thus indicated.

Much clear weather is wanted, and this means a site far removed from the paths of the principal storms, which cross the United States from west to east near the Canadian border and from south to north along the Atlantic coast. Great distance from storm centres is also favorable to sharp definition of star images, a prime requirement. As the unsteadiness of these images is naturally greater in the denser and more disturbed air of low altitudes, a high altitude is required, where the loss of light by atmospheric absorption is also low. But the site must not be too high, because of the extremely low temperatures and the consequent distortion of the telescope mirror when it is exposed to the sky at night (it is tightly enclosed in a nearly constant temperature case throughout the day). Local causes of disturbance, such as winds, electric lights, and so forth, must also be borne in mind.

Finally, the easy accessibility of cooperating laboratories and observatories is of vital importance. After previous study of these questions in selecting the site of the Mount Wilson Observatory thirty years ago, combined with the work accomplished since that time with many telescopes up to one hundred inches in diameter, it is clear that a site should be chosen not far distant from the many observatories, laboratories, and instrument shops in and near Pasadena. Although comparative telescopic tests of several neighboring mountain summits have been made during the past five years, a final decision has not yet been reached.

v

The question of auxiliary apparatus and facilities, both for attachment to the telescope and for the interpretation of the observations obtained, is one of the most important problems before us. The Observatory Council, placed in full charge of the entire project by the Trustees of the California Institute, comprises Robert A. Millikan, Director of the Norman Bridge Laboratory of Physics; Arthur A. Noyes, Director of the Gates Laboratory of Chemistry; Henry M. Robinson, long experienced in national and international economic affairs; Walter S. Adams, Director of the Mount. Wilson Observatory of the Carnegie Institution of Washington; and the writer, Honorary Director of the Mount Wilson Observatory of the Carnegie Institution of Washington (chairman). John A. Anderson, the executive officer of the Council, has had long experience as a physicist and astronomer at Johns Hopkins University and the Mount Wilson Observatory. We are also aided by a large group of mathematicians, astronomers, physicists, chemists, and engineers, selected from the research staffs of the Mount Wilson Observatory and the California Institute and from universities and other institutions in this country and abroad. A few specific illustrations will make clear our procedure.

While it was recognized that an exceptionally short focus for the 200inch mirror was desirable in order to concentrate the feeble light of the most remote celestial objects, we were faced by the fact that the sharply defined field of such a mirror is very small. Ross of the Yerkes Observatory was accordingly asked to devise a new type of correcting lens, to mount before the plate and enlarge the field of good definition. He has had remarkable success in this work, as tests of his lenses with the large reflecting telescopes on Mount Wilson abundantly prove. We also wished to multiply the efficiency of the new telescope for the photography of the very faint spectra of distant objects, especially for measuring the velocity of the remote spiral nebulæ. For this purpose an extremely shortfocus lens was needed, far faster than the most rapid movie lenses, the best of which had been tried on Mount Wilson. Rayton, of the Bausch and Lomb Optical Company, succeeded in devising an incredibly fast lens, on the principle of a microscope objective, with an aperture of two inches and a focal length of but little more than one inch.

It is with this lens, attached to the spectrograph of the 100-inch reflector, and extending earlier work to more distant objects, that the law of the ‘ expansion of the universe ’ has been found by Hubble and Humason. At present, through the cooperation of Jackson, Moore, and Bracey of London, a still more rapid lens of similar type is being developed for us by the British Scientific Instrument Research Association.

Other methods of increasing the efficiency of large telescopes include the improvement of photographic plates and of other sensitive detectors of faint radiation, such as thermocouples, photoelectric cells, and radiometers. We have therefore sought to stimulate such work, and have found great satisfaction in the splendid results obtained by Mees and his associates in photography, Pettit and Nicholson with the thermocouple, Abbot and Sinclair Smith in radiometry, and Stebbins, Dunham, and Whitford in the development of the photoelectric amplifier. With the new Eastman plates it is now possible to record solar, stellar, and planetary spectra in the extreme infrared, while the photoelectric amplifier used on Mount Wilson with the 100inch telescope has recently shown the Great Nebula in Andromeda to be twice as wide as it was formerly supposed to be. Without mentioning other similar advances, it is easy to imagine the great gain in space-penetrating power, only partially foreseen at the initiation of this enterprise, now promised by the 200-inch telescope.

In his most recent book, The Dawn of Conscience, Breasted gives a striking historical picture of human experience and personal character gradually and slowly arising out of the developing universe. His reasoning is based on observation reaching far behind the dawn of written Egyptian history. Though we can find no convincing evidence of man’s presence on bodies other than the earth, it would be strange if life did not exist, in lower or possibly higher forms, on some of the planets that probably revolve about many distant stars. Breasted and those who look back through geological time to the earliest ages of the earth are exploring the past. Astronomers are doing likewise, in a vastly extended region. They have no expectation of

detecting signs of life, but they can study the evolution of the universe in which the earth plays a part. Although light travels through space at the rate of 186,000 miles per second, we see the sun as it was eight minutes ago, Arcturus as it looked when the light now entering our eyes left it forty years ago, the distant stars of the Milky Way as they were thousands of years ago, the nearer spiral nebulæ as they were a million years ago, the remote nebulae as they were thousands of millions of years ago. In other words, the heavens as we see them do not appear as they existed at any one time, but rather in the form of a composite picture, covering a period of countless years.

Is it surprising that we still push our observations outward, urged by the same desire for knowledge that has persisted through so many centuries? Or that Poincaré, recognizing what astronomy has done to stimulate all forms of research, once queried, in La Valeur de la Science: ‘What would our modern civilization have been if the earth, like Jupiter, had always been surrounded by clouds?’