Annual Report of the President of the University on behalf of the Regents to His Excellency the Governor of the State of California, 1916-1917
Lick Astronomical Department--Lick Observatory
MOUNT HAMILTON, July 1, 1917.
To the President of the University,
SIR: I have the honor to submit herewith my report for the period July 1, 1916, to June 30, 1917.
All of the instruments of the Observatory are in excellent condition. The 36-inch refracting telescope has been used intensively throughout every good night, except three or four nights in midwinter when the prevailing low temperatures did not permit the use of the hydraulic system which operates the movable floor in the dome. The Crossley reflecting telescope has been used intensively during the night hours when the moon was absent or thinly crescent. Useful photographic exposures are prevented, it is well known, when the sky is bright with moonlight.
A new mechanical device for guiding with the Crossley reflector when photographing very faint moving objects was designed by Dr. Curtis and constructed in 1916. It is a great improvement upon the former device in the positive character of the motion, and in total freedom from serious error and from failure to work.
The eclipse instruments and auxiliary supplies which were left in the keeping of the National Observatory at Pulkowa, Russia, following the Russian solar eclipse of 1914, have been a source of anxiety, partly because many letters of inquiry addressed to the Observatory authorities failed to bring any response until the spring of 1917, but chiefly because it was feared the instruments would not be available for observing the total
The eclipse of next year will occur in a month when the weather conditions are promising and when the sun is at a good altitude. It is hoped that the Observatory may arrange for the sending of a well-equipped expedition to observe the interesting phenomenon.
At this time last year it was feared that the D. O. Mills Expedition to the Southern Hemisphere would have to close in the spring of 1917 on account of lack of funds. The generous contributions of Mr. D. O. Mills during the years 1900-11 and of Mr. Ogden Mills during the years 1911-17 had amounted to a total of approximately $109,000, and under the disturbed financial conditions arising from the war Mr. Ogden Mills decided that he could not continue the support. I am pleased to report that seven friends of astronomy, including Mr. Ogden Mills, have generously provided funds to extend the life of the expedition through five additional years, 1917-22. These are: Mr. William H. Crocker, Mrs. William H. Crocker, Mr. F. W. Bradley, Mr. A. B. Spreckels, Mr. W. B. Bourn, Mr. Gordon Blanding, and Mr. Ogden Mills. The observing program for the observatory on the summit of Cerro San Cristobal in the northeastern suburbs of Santiago, Chile, has accordingly been extended. The expedition is in charge of Acting Astronomer R. E. Wilson. Mr. A. A. Scott, Assistant at Santiago, resigned, to take effect in June, 1917, and his successor, Mr. Charles Morse Huffer, of Albion College and the University of Illinois, will leave for Chile in July.
The first chairman of the Lick Observatory Committee of the Regents of the University was Mr. Timothy Guy Phelps, of San
During the past two years the major part of our resources have been devoted to studies of the nebulae, both the so-called gaseous nebulae, whose spectra consist chiefly of bright lines, and the spiral nebulae. Some of these studies have been completed and the results published. Several other studies will have been completed before the end of the present calendar year and the results are expected to appear in the Semicentennial Publications of the University. The pursuance of these greater problems has left no time in the past year for inaugurating new lines of research except as these have related to minor problems.
Mr. Curtis's photography of the planetary nebulae, mentioned in my last report, has been completed by the securing of 127 additional negatives. The program includes seventy-four objects, visible from Mount Hamilton. Most of these objects are too small to permit of direct photographic enlargement for purposes of publication. In addition, there are very great differences of intensity between the brighter central parts of the nebulae and the fainter outlying structures, so that, in general, a single photograph of one of the nebulae cannot convey adequate information as to the structural details. Mr. Curtis adopted the plan of taking a number of exposures of each object with varying exposure times and of making a composite drawing from the series of images. This was done for all the objects in the group except for a few of the larger planetaries where photographic enlargements were satisfactory. The half-tone blocks have been completed for all of these planetary nebulae, and the
In the progress of this work Mr. Curtis has been able to recognize that several objects previously described merely as nebulae are, in fact, of the planetary type. One of these is the nebula, N.G.C. 7293, whose angular diameter is 15', by far the largest of all the known planetaries.
Fewer than 150 planetaries are known to exist. Astronomers are familiar with the fact that the planetaries are nearly all located within or near the Milky Way. There are a few exceptions to the rule. Mr. Curtis's statistical study of their distribution in the sky with reference to their angular diameters led to the interesting conclusion that the planetaries having the smaller angular diameters preferentially group themselves near the central line of the Milky Way, those of medium size have a wider distribution, and the larger planetaries are fairly evenly distributed over the sky. These conditions are in harmony with the assumption that the planetary nebulae are distributed somewhat at random within our great ellipsoidal stellar system; those farthest away will in general be seen nearest the central line of the Milky Way and have the smallest angular diameters; and those relatively very near our solar system will in general have greater angular diameters and be seen in projection in directions making a great variety of angles with reference to the central plane of our system.
Mr. Curtis's representations of the planetary nebulae have been of great value to those of his colleagues who have been studying the planetaries along other lines, to be described later.
There is perhaps no class of celestial objects concerning whose constitution we have so little definite information as the spiral nebulae. It is an important though somewhat neglected duty that as many as possible of the larger spirals should be photographed on a large scale. Such photographs would not only furnish data for studies of the geometric forms of spirals, but
| Spiral nebulae . . . . . | 477 |
| Diffuse nebulae . . . . . | 47 |
| Planetary nebulae . . . . . | 74 |
| Globular star clusters . . . . . | 43 |
| Other star clusters . . . . . | 11 |
This tabulation neglects the thousands of very small nebulae found on the plates, and, in fact, includes only those of sufficient size to be valuable for studies of nebular structure. It is planned to continue this work until between 200 and 300 additional bright or large objects have been recorded. The region of the sky richest in spirals is unfortunately so situated as to be available for observation to advantage only in the spring months, when observing conditions are the poorest, and accordingly the program cannot be completed for several years.
The great value of this extensive collection, believed to be by far the most extensive in existence on such a large scale, has been shown recently in various ways. It has afforded data for the study of absorption or occulting effects in the spiral nebulae. It is characteristic of the spiral nebulae that they are of enormous dimensions in what we may call their equatorial diameters
In March, 1917, while studying the Crossley photographs of nebulae, Mr. Curtis discovered a “new star” of about the fourteenth magnitude which had appeared in the spiral nebulae N. G. C. 4527 shortly before March 20, 1915, and which has since disappeared. The occurrence of such novae in the spiral nebulae, of which this is the third example, is a fact of great interest, and appears to furnish weighty evidence in favor of the theory that the spiral nebulae are, in effect, separate and very remote universes, vast congeries of stars so distant that the most powerful instruments are inadequate to resolve the individual stars.
It has long been known that the spiral nebulae are scarce in and near the Milky Way and very plentiful in the remainder of the sky. In fact, they become plentiful as one proceeds toward the poles of the Milky Way. This peculiarity of distribution is one of the most remarkable facts recorded in the literature of astronomy, and the search for the explanation is in the forefront of present astronomical inquiry. Why do the spiral nebulae seem to avoid the Milky Way? Are they within our stellar system, or are they distant and separate universes of stars having no geometric or dynamic connection with our stellar system? Are those outer systems clustered in two gigantic volumes of space, our stellar system happening to lie between them? Are those distant systems distributed somewhat at random and actually existent in all general directions from our system, their apparent absence in the direction of the Milky Way regions finding its explanation in the existence of intervening matter which prevents us from seeing them? Two years ago, on my suggestion, Mr. Sanford, Martin Kellogg Fellow in the University, undertook to make such study of these questions as the existing observed facts, and the time of the Crossley reflector available for securing additional facts, would promise to make useful. This study and the provisional conclusions therefrom are described in Lick Observatory Bulletin No. 297. Quoting Dr. Sanford's concluding paragraph:
“Briefly stated, an arbitrary and general distribution of the spiral nebulae is harmonized with the distribution that presents itself to observation, by means of the hypothesis of an obstructing medium irregularly distributed throughout the Galaxy. The solar system is assumed to lie to the south of the median plane of the Galaxy and near its short axis, but within the realm of the obstructing material.”
It is not affirmed by Mr. Sanford that this conclusion has been definitely established, but we may safely say that the evidence presented by him, combined with several other lines of evidence, notably that collected by Mr. Curtis as to the existence of occulting or absorbing matter in the outer reaches of the spiral nebulae, makes the explanation both plausible and probable.
The extensive program of measuring the motions of approach and recession of the gaseous nebulae, at Mount Hamilton by Messrs. Campbell and Moore, and at the D. O. Mills Observatory in Chile by Dr. Wilson, is nearing completion. A dozen nights devoted to this subject at Mount Hamilton and twenty nights at Santiago, Chile, in the fall months of 1917 should exhaust the list of all such objects bright enough for observation. The grouping of these objects in and near the Milky Way, that is, at two opposite parts of the sky for the observers in each hemisphere, and the long exposures required, extending in some cases up to thirty hours, have prevented the more rapid completion of the investigation. The velocities of 124 planetary nebulae and other nebulae with bright-line spectra have been determined to data. In the early winter, after the remaining observations shall have been secured, the resulting velocities will be discussed both statistically and individually and the work will be described in a Semi-Centennial Publication.
The investigation of the rotational and internal motions of planetary nebulae, begun in the latter part of 1915 and described in my last report, were conducted with fruitful results in the past year. In fact, all of the planetaries visible from Mount Hamilton which are bright enough to permit of observation with high dispersion exposures have been observed in this connection.
Several of the larger planetary nebulae, notably N.G.C. 7662 and N.G.C. 2392, have spectra whose lines are strongly doubled. We have made a study of this phenomenon from the point of view of all possible explanations which suggest themselves to us, chiefly by means of polarization tests. Using high dispersion and various pieces of auxiliary apparatus for detecting different qualities of polarized light, we have been led to decide against the presence of a magnetic field in the nebulae, known as the Zeeman effect, and to recognize the possible presence of an electric field responsible for the so-called Stark effect. However, a simpler explanation seems more probable: that the doubling of the lines and their other characteristics may be due, first, to the broadening of the lines, arising either from the motions of approach and recession of the particles or from a relatively high pressure of the gases in the central volumes of the nebulae, and the introduction of a medial absorbing line upon the broadened bright line, the absorption proceeding from an outer stratum of gas of lower temperature. All of the several planetaries in which this peculiar form of line has been observed belong to a particular
Messrs. Moore and Campbell have brought almost to completion their study of the motions of approach and recession of various parts of the Great Nebulae in Orion. Forty-three long-exposure spectrograms were obtained for this purpose within the year. A few additional exposures on the fainter outlying parts of the nebula remain to be secured next November and December prior to the publication of the results. In addition to confirming the observations of last year, we have established that the detached nebulous structure 7' north and 4' east of the Trapezium group of stars in the center of the Orion Nebula is receding from our position in space with a speed of about 8 km./sec. with reference to the speed of the Trapezium region.
A special study of the two planetary nebulae N.G.C. 6543 and N.G.C. 7009 as to their rotations, internal motions and photometry has been made by Dr. Green, and published in Lick Observatory Bulletin No. 298.
In addition to the nebular spectrograms, 238 exposures for determining the motions of approach and recession of stars have been secured at Mount Hamilton within the year. Many of these are of spectroscopic binary stars or other stars of special interest.
The work of the year in Chile consisted of about twenty long-exposure spectrograms of nebulae and of 480 spectrograms of stars. All of them have been measured by Dr. Wilson and Mr. Scott. The additional observations of the bright-line nebulae in the Greater Magellanic Cloud are confirmatory of the preceding years' work as to their abnormally high recessional velocities. No exceptions to the rule have been found. The hypothesis that the Greater Cloud as a system is receding rapidly and is dynamically separate from our Milky Way system has been given added strength. Dr. Wilson has found that two or three stars in the Greater Cloud whose spectra are of the Wolf-Rayet, or special bright-line, type appear to be receding from us with high velocities of the same order as the nebulae. He has measured
Dr. Moore has published a list of six spectroscopic binary stars discovered by virtue of their variable velocities as recorded on the spectrograms secured by him when in charge of the D. O. Mills Expedition.
Similarly, Dr. Wilson has published a list of four spectroscopic double stars, and a considerable list of binaries found by him awaits publication.
Dr. Paddock has announced the binary character of six variable stars whose spectra were observed by him several years ago when an assistant at Santiago, Chile. He has likewise completed and published the orbit of the interesting spectroscopic binary system h Centauri, on the basis of observations secured by him in Chile.
Acknowledgments are due to Messrs. Paddock, Shane, Scott, and Neubauer for assistance in securing many of the exposures referred to above, and to Miss Hobe, Dr. Paddock, and Mr. Scott for very extensive help in the measurement of the plates.
The very important study of the structure and composition of the planetary nebulae by Mr. Wright, described in last year's report, has been carried through the present year, chiefly with the slitless quartz spectrograph in connection with the Crossley reflecting telescope. The program includes all the planetary nebulae which it is practicable to observe with this instrumental equipment. It is hoped that this programme of observation will be completed in July and August, 1917. The results confirm the view that very high temperatures are an important characteristic of the nuclei of these nebulae, a fact which is of significance in every theory of stellar evolution. The detailed results of nebular composition and structure proceeding from this work are in preparation for issue in the Semicentennial Publications.
Mr. Tucker has extended his investigation upon the dependence of atmospheric refraction upon the time of sunset and sunrise. One thousand observations of the zenith distances of stars made by him with the meridian instrument were used in the solution of this problem. He has found that the atmospheric refractions determined at the Pulkowa Observatory of the Russian government, and extensively used at many observatories in correcting their meridian observations for prevailing atmospheric conditions, are too large to represent the refractions at Mount Hamilton during the night hours and too small to represent them during the daylight hours. The observed refractions at Mount Hamilton agree in size with the Pulkowa refractions at one hour before sunset and at one hour after sunrise. The amount of the variation is close to one per cent of the total refraction correction; a quantity entirely too large to be neglected. Mr. Tucker's discussion of the subject indicates that there is an essentially uniform progressive variation for the period one hour before sunrise to four hours after sunrise and a similar reversed variation for the period four hours before sunset to one hour after sunset. It is the custom to compute the refractive effect for an observed star upon the basis of the barometer and thermometer readings just outside the observing room at the time of making the stellar observation. It would seem that the barometer and thermometer readings represent the atmospheric conditions satisfactorily only at the two instants, one hour after sunrise and one hour before sunset, and that at other times of the day slight but sensible corrections are required in order to represent the facts.
Early in 1917 Mr. Tucker began to observe the accurate position of 1074 selected stars from the Harvard northern Zone of the Astronomische Gesellschaft Catalog, these observations to serve as the basis for determining the positions of great numbers of additional stars in the same zone of the heavens by photographie methods. The photographs and their measurement are to be made by the Allegheny Observatory, and our share of the work has been undertaken at the request of Director Schlesinger of Allegheny. More than one-third of the selected stars have been
It is of interest to note that Mr. Tucker's industry has led to securing about 40,000 meridian circle observations to determine the extremely accurate places of more than 10,000 stars during the period of his service, which began in the year 1893. The immense task of reducing these observations has been carried through by him alone, with negligible exceptions. The corresponding discussions of the results have been made and the data issued in three volumes of publications of the Lick Observatory. In this same period about 40,000 readings have been made upon the graduation lines of the divided circles in order to determine the size and sign of the graduation errors.
From July 1, 1916, to March 15, 1917, using the 36-inch refractor about two nights per week, Dr. Aitken has continued his studies of double stars. Fifteen new pairs were discovered in this interval, though very little effort was devoted to the search. He has secured 752 complete sets of measures of the relative positions of the pairs of stars forming the doubles. These relate chiefly to the doubles discovered by himself. His remeasurements of the doubles after an average interval of eleven years following discovery show definite motion in about one-fifth of the pairs thus far measured, and what we may call rapid motion in about one-tenth of them. He has at the same time continued his observations of the more difficult well-known double stars and has made interesting deductions as to the orbits of several especially interesting pairs. He found, for instance, that the well-known binary, Zeta Boötis has an orbit possessing the remarkably high eccentricity 0.96. Three orbits have been determined and published.
Mr. Shane is investigating the changes which occur in the spectra of certain variable stars as functions of their brightness.
Micrometer observations of the positions of comets have been made by Messrs. Aitken and Shane as required by the Berkeley Astronomical Department for the determination of the orbits of comets just discovered.
It is not practicable to refer to several investigations of a minor nature made within the year.
Dr. Curtis was absent during the first five weeks of the academic year as officer in charge of astronomical teaching at the Summer Session of 1916 in the University of California.
Dr. Aitken has been absent on leave from March 15, 1917, due to return on July 15. In this interval he has delivered more than twenty lectures on astronomical subjects in universities and other institutions of the Middle and Atlantic States; he has secured valuable information at Harvard College Observatory on the character of the spectra of double stars through the courtesy of Director Pickering; and he has engaged in the preparation of the manuscript for a volume on “The Binary Stars,” which should be ready for the printer about the middle of the coming winter.
The six Adolfo Stahl Lectures in the Astronomical Society of the Pacific were delivered by Messrs. Campbell, Aitken, and Curtis in San Francisco during the winter and spring months. The annual lectures in the Berkeley Astronomical Department in the spring of 1917 were delivered by Messrs. Campbell and Wright. A considerable number of additional lectures were delivered within the year in central California by Messrs. Campbell, Aitken, Curtis, and Moore.
The honorary degree of Doctor of Sciences was conferred upon Dr. Aitken by Williams College at the June Commencement.
As retiring President of the Pacific Division of the American Association for the Advancement of Science, Mr. Campbell delivered an address in San Diego in August, 1916, on “What We Know About Comets.” As retiring President of the American Association for the Advancement of Science, Mr. Campbell delivered an address on “The Nebulae” in New York City, on December 26, 1916.
It is well known that increased financial resources for the Lick Astronomical Department are highly desirable, both to widen and intensify the scope of our research activity and to compensate for the immensely reduced purchasing power of
The indications are that the fulfilling of various duties growing out of the state of war will affect the output of investigational results in the coming year.
Courtesy of University Archives, The Bancroft Library, University of California at Berkeley, Berkeley, CA 94720-6000; http://bancroft.berkeley.edu/info
http://content.cdlib.org/view?docId=hb1r29n73v&brand=oac4
Title: 1916-1917, Annual Report of the President of the University on behalf of the Regents to His Excellency the Governor of the State of California
By: The Regents of the University of California (System), Author, Wheeler, Benjamin Ide, 1854-1927, Author
Date: December, 1917
Contributing Institution: University Archives, The Bancroft Library, University of California at Berkeley, Berkeley, CA 94720-6000; http://bancroft.berkeley.edu/info
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Material in public domain. No restrictions on use