Popular Science Monthly/Volume 86/March 1915/Astronomy on the Pacific Coast
THE
POPULAR SCIENCE
MONTHLY
MARCH, 1915
| ASTRONOMY ON THE PACIFIC COAST |
By Professor RUSSELL TRACY CRAWFORD
THIS subject brings instantly to the mind's eye the Lick Observatory on Mount Hamilton, and the Solar Observatory on Mount Wilson, as they are two of the greatest astronomical observatories in the world, and probably the best generally known of all. The one is an asset of the Pacific coast, probably accidentally, the other was placed there as a result of mature deliberation after thorough investigation of many locations. In addition to these two wonderful institutions there is in process of construction a third great observatory near Victoria, B. C, which, when completed, will contain the second largest reflecting telescope in the world. It is evident, therefore, that conditions on this coast are extremely favourable for developing the practical side of astronomy. On the other hand, the theoretical side of the subject is by no means to be lost sight of, as I shall point out.
In the early days before the erection of the Lick Observatory, the only astronomical work on the Pacific Coast was that done by the U. S. Coast and Geodetic Survey under the able direction of the late Professor George Davidson. This was not astronomical work as such, but merely the solving of such astronomical practical problems as were incident to the regular work of the survey. The first real scientific astronomical investigations came with the advent of the Lick Observatory.
This institution is the gift of James Lick, a California pioneer, who had amassed a fortune of several million dollars.
On July 16, 1874, he executed a deed of trust which devoted the entire sum to public purposes.
Among the provisions of the deed is one that directed the trustees
to expend the sum of seven hundred thousand dollars for the purpose of constructing. . . a powerful telescope, superior to and more powerful than any telescope ever yet made, with all the machinery appertaining thereto. . . .
He left the trustees certain discretionary powers as to its location
with the proviso, however, that "the same must be located within the state of California."
Just why Lick provided for this telescope and observatory will probably never be known. While I can not recall my authority, I have a very distinct recollection of having heard it stated that the idea was first suggested to him and frequently urged upon him by Professor George Davidson, Concerning this point, however, the director of the Lick Observatory writes,[1]
The question, "What induced Lick to provide for a great telescope?" has never been satisfactorily answered; but there is no reason to doubt that he came to this determination without conscious suggestion from others.
After having several sites tested the trustees decided upon Mount Hamilton, California, as the best location for the observatory. Active work was begun in 1879, and the observatory was completed and ready for regular work in 1888. The plant cost all but $90,000 of the amount set aside for it. The observatory and this balance were turned over to the regents of the University of California by the trustees June 1, 1888; and since then it has been an integral part of the university.
The principal instruments of this observatory are the great 36-inch refractor, a 6-inch Repsold meridian circle, provided by the Lick Trust, and the 3614-inch reflector, a gift from Edward Crossley, Esq., of England. Besides these there is a host of smaller instruments and auxiliary apparatus. I can not go into details here concerning the instruments, but I wish to mention one which has an important bearing upon the subject of this article. It is that the magnifying power of the great refractor may be made to be as much as 3,000 diameters. When one considers that everything in the line of sight of the telescope is magnified by this amount, it becomes evident that, to be efficient, the telescope must be located at a site where the atmosphere through which the line of sight passes is extremely steady, for any little atmospheric disturbance will be magnified to this amount and destroy what is called the "seeing," giving a poorly defined image of the star or object under observation. And it is principally on account of the splendid atmospheric conditions on the Pacific coast, especially on some of the moderately high mountains, which make excellent "seeing" possible that observational astronomy here has been able to make such tremendous strides.
For the efficient use of a great telescope its location must be in a region of great atmospheric calm, where the sky is clear and transparent, with little wind, and where the number of days and nights of a year during which such conditions do not exist is small. For some reason, the "seeing" conditions at Mount Hamilton during the day are not of the best; but at night excellent conditions are found on a large
majority of the nights of a year, and many nights yield "seeing" that might be considered perfect. A glance at the illustrations showing the mountain as seen from the east and from the west will make it evident at once why these conditions obtain. With the exception of a saddle running eastward, the land slopes away rapidly from the summit down into deep valleys, so that there is but little opportunity for heat waves radiated from surrounding land to mount to the atmosphere above the observatory and create atmospheric disturbances. The mountain is not so very high (4,209 feet above mean sea level), but it is high enough to hold the observatory in an atmosphere free from dust, smoke and fog. Being near the ocean, fogs are very frequent at certain seasons over the valleys in this region. It is seldom, however, that they mount high enough to envelop the observatory. Many evenings and early mornings fog completely fills the surrounding valleys, so that the observatory seems to rest on an island in a vast sea of fog. Often peaks only a few hundred feet lower than Mount Hamilton are covered by the fog, yet the work with the great instruments is uninterrupted. The picture "Fog in the Valleys at Sunset" gives a better idea of this condition than I can describe. In such a location as this the 36-inch refractor can be used with its maximum power a large portion of the time. In less favorable localities even larger instruments would not be so efficient.
It is one thing to have an excellent plant, and it is another thing to have men skillful enough to operate such a plant effectively. A very proficient marksman can not do very much damage with a blunderbuss, and one unskilled will not be able to produce any good results from the best modern artillery; but an expert behind a Krupp can produce a high percentage of effective hits. And so it is with the Lick Observatory. Not only is it a wonderful engine of science, but also it has been very fortunate in the astronomers who have operated it.
I can not here go into the details of all that has been done at the Lick Observatory, but the following extracts from "A Brief Account of the Lick Observatory of the University of California," prepared by the director of the observatory, 1914, give an idea of the principal things of general interest that have been accomplished in the quarter of a century of its existence:
1. To the four bright satellites of Jupiter discovered by Galileo in 1610, the Lick Observatory has added four satellites.
2. Twenty-nine comets have been discovered. Nineteen of these were unexpected, and ten were periodic comets whose return had been predicted.
3. The first great success in photographing comets and the Milky Way were made here.
4. About 4,400 double star systems have been discovered.
5. Irregularities in the motions of the first magnitude star Procyon had led the celebrated German astronomer Bessel, three quarters of a century ago, to predict that Procyon had a companion sun revolving around it. This companion was discovered with the Lick telescope.
6. Spectographic observations of stellar motions have shown that the solar system is traveling through space, with reference to the general stellar system, at a speed of about twelve miles per second.
7. The Mount Hamilton and Santiago[2] spectographic observations of stellar motions have shown that stars effectively young are traveling slowly, middle aged stars more rapidly, and old stars more rapidly still; that is, that the velocities of the stars increase with their effective ages.
8. Observations have established that those nebulæ known as planetary nebulæ are traveling through space with average speeds even higher than the average speeds of the stars. It had previously been supposed that these nebulæ represented a stage of existence antecedent to the stellar age. The high velocities of these objects have created the opinion that they have more probably been formed from stars which have been overtaken by catastrophes, such as collisions with other celestial objects.
9. The North Pole Star was found to be a triple star, in 1899, by means of spectrographic observations. The first magnitude star Capella was discovered to consist of two stars revolving around their center of mass in 104.1 days, the two nearly equal components being inseparable in our largest telescopes.
10. In the same manner about 250 spectroscopic binary stars have been found at Mount Hamilton and Santiago.
11. A study of the orbits of spectroscopic binary stars has established that the component stars in a system whose spectrum indicates early age are relatively very close together, requiring very short periods of revolution, and that the orbits are nearly circular. In systems whose spectra show them to be of greater effective ages, the distances separating the components are successively greater, on the average, and their orbits are more eccentric. The observed facts on the subject are fully confirmative of existing mathematical theories of the evolution of double star systems.
12. The Crossley reflecting telescope established for the first time the tremendous advantage of this form of telescope in the photography of certain classes of celestial objects, such as nebulæ, star clusters, etc.
13. Before the Crossley reflector was in use about 10,000 nebulæ had been discovered at various observatories. A few dozens of these were known to be spiral in form. The Crossley photographs led to the discovery of many hundreds of additional nebulæ in the extremely small part of the sky covered by the photographs. It was a simple matter to calculate that certainly 120,000 and possibly half a million nebulæ await discovery whenever time can be spared for the Crossley reflector to undertake this work. These photographs led to the unexpected discovery that a majority of the nebulæ are of spiral form—undoubted evidence of their rotation.
14. The extensive series of photographs of the minor planet Eros and surrounding stars, with the Crossley reflector, led to a new and accurate determination of the distance from the earth to the sun.
15. Eight total solar eclipses have been successfully observed by expeditions whose expenses were defrayed by friends of the observatory.
16. It has been shown that the new stars appearing in recent years have been converted into nebulæ, and later, in many cases, into extremely faint stars of apparently normal condition.
17. Many thousands of extremely accurate positions of the stars have been secured with the meridian circle.
18. Very extensive observations of double stars, comets, planets, and satellites have been made.
19. A large number of orbits have been computed for visual double stars, spectroscopic binary stars, comets, and asteroids.
20. Extensive additions have been made to our knowledge of the spectra of nebulæ, comets, new stars, and stars of special interest.
21. Important studies of the spectra of spiral nebulæ and star clusters have been inaugurated.
22. An atlas of the moon was made in the first year of the observatory's existence, on the basis of photographs obtained with the large telescope.
23. The motions of approach and recession of about 1,500 naked-eye stars, distributed over the entire sky, have been observed with the 36-inch refractor at Mount Hamilton and the D. O. Mills reflector at Santiago.
24. Spectroscopic observations at Mount Hamilton and on the summit of Mount Whitney have shown that the atmosphere of Mars is of low density, probably much less dense at the surface of Mars than the earth's atmosphere is at the summit of the highest peak in the Himalaya Mountains. These observations have established likewise that the quantity of water vapor in the atmosphere of Mars above, say, a square mile of its surface, must be very slight as compared with the quantity of water vapor in the earth's atmosphere above an equal area.
Mount Wilson Solar Observatory.
The wise economical policy of this observatory is to engage principally in those investigations which can not be carried on with smaller and less effective instruments. Much that could be done there is left to smaller institutions. The great instruments are used only for the problems that demand their great power. And these are quite sufficient to keep them in constant use.
Turning now to the Mount Wilson Solar Observatory we find a unique institution. As its name implies, it is an observatory erected primarily for the study of the sun.
This recommendation resulted ultimately in the erection of the Solar Observatory by the Carnegie Institution by which it is supported. Various sites in Arizona and in southern California were tested, and the summit of Mount Wilson (nearly 6,000 feet above sea-level) near Pasadena in southern California was selected. In the choice of a site for this observatory excellent "seeing" conditions in day time as well as at night were of primary importance. Such conditions were found to exist on Mount Wilson.
For director of the observatory a very wise choice was made in Dr. George E. Hale. It is due principally to his genius and untiring efforts that this wonderful plant has been designed and brought to its present high state.
Dr. Hale points out that the term "solar observatory" is to be used in a broad sense,
Such an observatory, whose primary object is "to apply new instruments and methods of research in a study of the physical elements of the problem of stellar evolution," must of necessity have as complementary parts of its equipment a physical laboratory and an adequate machine shop. These two parts have been supplied and are located in Pasadena. Here not only are smaller pieces of apparatus made and repaired, but also the enormous discs of glass for the 60-inch and the 100-inch reflectors have been figured and tested.
The instrumental equipment of the solar observatory is naturally very complete. In addition to the numerous smaller pieces of apparatus there may be mentioned in particular the Snow telescope, the two tower telescopes, and the monster reflectors.
The Snow telescope consists of two 24-inch concave mirrors of different focal lengths (when either one is in use the other is easily put out of the way) mounted well above the ground in such a way as to throw the sun's rays horizontally under a louvre covering to the spectroscope or other apparatus, where they are analyzed. Soon after this instrument was in operation Dr. Hale conceived the idea of mounting the coelostat at the top of a tower, and sending the rays vertically downward to the spectroscope so as "to avoid disturbance of definition caused by heated currents of air arising from the ground," He therefore had designed and erected a 65-foot tower for this purpose. This was very successful. Then desiring a greater focal length than could be obtained with this height, be had built a second tower 150 feet high. Under this tower a well was excavated to the depth of nearly 80 feet, thus providing for a possible focal length of about 230 feet. The 150-foot tower is of ingenious construction. It is a tower within a tower. The main structure which supports the coelostat at the top is completely sheathed in an encasing tower which supports the dome, so that there is complete protection from the wind. When one looks at the tower he sees only the framework of the sheathing. This great tower telescope is a most efficient and satisfactory instrument.
There is no larger telescope in operation to-day than the 60-inch reflector, the reflecting surface of which was ground by Mr. Ritchey in the shop at Pasadena. The remarkable photographs of nebulæ that have been made with it speak loudly in praise of its efficiency. This instrument is soon to be supplanted in its proud position of size by the 100-inch reflector, the gift of Mr. J. D. Hooker, which is nearing completion. The figuring of the enormous block of glass has also been done by Mr. Ritchey. The present state of the building to hold this great reflector is shown in the accompanying picture. The completion of this, the largest telescope in the world, will undoubtedly mark an epoch in observational astronomy. Its light-gathering power will be nearly three times as great as that of the 60-inch, and more than seven times that of the Crossley reflector of the Lick Observatory which in its turn fifteen years ago marked an epoch. If "half a million nebulæ await discovery" with the Crossley, think of the possibilities awaiting this giant!
In the ten years of its existence the results of the investigations of the Mount Wilson Solar Observatory have been very numerous and most valuable. I have not space here even to enumerate them. Every annual report of the director contains a summary of the principal results of the year. The number of such results is noticed to increase from year to year. In the last Annual Report (1913) seventy-two results are summarized. Most of these are of such a technical nature that they are of interest only to the scientist. Of the results of general interest I may mention the discovery of magnetic fields in sunspots; the fact that "the sun is a magnet, with magnetic poles at or near the poles of rotation"; "the polarity of the sun corresponds with that of the earth—a conclusion which may prove to have an important bearing on theories of terrestrial magnetism"; "the evidence that has been amassed in support
of the view that light is absorbed in space." The last, as Dr. Hale points out
The investigations of the solar observatory are carried on not only by the regular staff, but also by other scientists who are invited to make use of the wonderful equipment there.
The Lick and the Mount Wilson Solar Observatories are the only ones at present on the Pacific coast whose energies are devoted wholly to investigations. A third will soon be in operation. This is to be an observatory eight miles north of Victoria, B. C., to house the 72-inch reflector of the Canadian government. Dr. Plaskett says:
This was written in June, 1914. A later report tells us that the disc has been received at Allegheny, and that work upon the mirror has been begun. When completed this will be the second largest reflector in the world.
In addition to these there are on the Pacific coast several small observatories connected with educational institutions whose principal use is to supplement by practical work the instruction in astronomy in these institutions. Among these may be mentioned the observatories of Pomona College, of Santa Clara College, Chabot Observatory of the Oakland High School (the Chabot Observatory is soon to be supplied with a 20-inch refractor). University of Washington, and the Students' Observatory of the University of California. Besides these there, is a small government observatory, a branch of the U. S. Naval Observatory, located at the naval station on Mare Island, used principally for time service and the regulation of the chronometers of the ships of the Navy. Finally, there are a few small private observatories wherein some amateur astronomers delight to "follow the courses of the stars."
Theoretical as well as practical astronomy is well fostered on the Pacific coast. Its chief development is to be found in the Berkeley Astronomical Department of the University of California. Here has been organized a thorough school of astronomy, than which, according to the late Professor Simon Newcomb, there is none better. Not only is the science taught at Berkeley, but also theoretical investigations are continually being carried on.
It is only natural that in a region possessed of such institutions as I have mentioned there should be a considerable interest in astronomy among the people. This interest is manifested principally through an organization known as the Astronomical Society of the Pacific with headquarters in San Francisco. This society resulted from the interest taken by a group of amateur astronomers and photographers in the total eclipse of the sun visible in California, January 1, 1889. It has a membership of several hundred who are interested in a general way in the science of astronomy. In addition to its meetings the Society issues bi-monthly its Publications of the Astronomical Society of the Pacific. The Society has been given two funds the interest from which is to be devoted to giving certain medals. One of these is known as the Donohue Comet Medal. One such medal is awarded to every discoverer of a new comet. The other is the Bruce Gold Medal, and is looked upon as one of the most important medals that can be awarded to an astronomer. It is awarded "for distinguished services to astronomy." The medal itself is a beautiful work of art, and is valuable both intrinsically and for what it symbolizes. The great value that astronomers attribute to this medal can be appreciated better when the manner of making the award is understood. The process is as follows: The directors of six observatories (Harvard, Yerkes, Lick, Berlin, Paris, and Greenwich) are each requested to nominate three men worthy to receive the medal in any given year. After these nominations are in it is usually found that six or seven names are presented to the directors of the Society from which then their choice for the medal must be made. If an award is made, therefore, it is to some one nominated by one or more (usually more) of the directors of six of the leading observatories of the world. There can be no doubt then that the recipient is justly entitled to this medal "for distinguished services to astronomy." That it is most highly prized by its recipients I quote from a typical letter of acceptance of the medal. The medallist writes, "I regard this distinction as the highest an astronomer can receive. . . ."
The results of the investigations at the Lick Observatory are issued in the Bulletins of the Lick Observatory for short articles, and in the Publications of the Lick Observatory (Volume XII. just issued) for the more extended work. Results from the Berkeley astronomical department are also issued in the Bulletins of the Lick Observatory, and one volume (VII.) of the Publications of the Lick Observatory is devoted to its investigations.
The Contributions from the Solar Observatory, Mount Wilson, California, issued by the Carnegie Institution of Washington, give to the world the results of the investigations carried on at the observatory on Mount Wilson and in the laboratories in Pasadena.
The Publications of the Astronomical Society of the Pacific I have already mentioned. The list of astronomical publications on the Pacific coast is made complete, I think, when I mention finally the Publication of the Astronomical Society of Pomona College, an interesting quarterly popular magazine issued by the astronomical students of Pomona College.
In preparing this account of astronomy on the Pacific coast I have drawn freely from "A Brief Account of the Lick Observatory" (fourth edition), and from the annual reports of the director of the Mount Wilson Solar Observatory, In conclusion I wish to express my thanks to the directors of these two observatories for their kindness in providing the illustrations.