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EDWIN HUBBLE died suddenly on September 28, 1953. An internationally known cosmologist, he was an Associate of this Society and always keenly enjoyed his visit to England where he and Mrs. Hubble had many warm friends. Check the page for more article options. This night occurred when he was just beginning observations on Mount Wilson. I received a vivid impression of the man that night that has remained with me over the years. He was photographing at the Newtonian focus of the 60-inch, standing while he did his guiding. His tall, vigorous figure, pipe in mouth, was clearly outlined against the sky. A brisk wind whipped his military trench coat around his body and occasionally blew sparks from his pipe into the darkness of the dome. "Seeing" that night was rated extremely poor on our Mount Wilson scale, but when Hubble came back from developing his plate in the dark room he was jubilant. "If this is a sample of poor seeing conditions," he said, "I shall always be able to get usable photographs with the Mount Wilson instruments." The confidence and enthusiasm which he showed on that night were typical of the way he approached all his problems. He was sure of himself of what he wanted to do and of how to do it.
It is not easy for a close associate to evaluate in a detached manner the work of Hubble and the contributions he made toward advancing the frontiers of knowledge. But no one could be intimately associated with him without having a sincere respect for his breadth of vision, his ever-active scientific curiosity, and his confident grasp of problems
Born in Marshfield, Missouri, on November 20, 1889, Hubble was the son of John Powell and Virginia Lee James Hubble. He received his B.S. degree at the University of Chicago in 1910; was appointed Rhodes Scholar from Illinois that same year, and went into residence at Queen's College, Oxford, between 1910 and 1913, receiving his B.A. degree in Jurisprudence at Oxford in 1912. At Oxford, he had won his Blue in track events and was a heavyweight boxer, having boxed in an exhibition match with the French champion, Georges Carpentier.
In 1913, when he returned to the United States, he was admitted to the bar in Louisville, Kentucky, and for a short time practiced law successfully. He had never, however, lost his deep interest in astronomy, and at the end of a year he returned to research at the Yerkes Observatory of the University of Chicago
It may be of interest that the title of his doctoral thesis was "Photographic Investigations of Faint Nebulae." In it, he considers the possible classification of nebular types, states that the planetaries are probably within our sidereal system, while the great spirals apparently lie outside our system, and says, "These questions await their answers for instruments more powerful than those we possess." The thesis is almost prophetic of his career.
Dr. George Ellery Hale, on a visit to Yerkes, offered him an appointment on the staff of the Mount Wilson Observatory, where the 60-inch was in operation and the 100-inch was under construction. But in April 1917, the United States entered the war. Hubble, who felt that the best way to see a war was in the Infantry, enlisted immediately as a private, although it meant sitting up all night to finish his doctor's thesis and taking the oral examination the following morning. He served with the American Expeditionary Force in France as a major in command of the Second Battalion, 343rd Infantry, 86th Division. After the Armistice, he remained for an additional year of duties in Europe. In the autumn of 1919, he returned to the United States, notified Dr. Hale that he was free to accept his offer, which had remained open, and came on to Mount Wilson
A brief summary of the work accomplished by Hubble can emphasize only the highlights. His first line of research at Mount Wilson had to do with a general study of galactic nebulae. One of his papers on this subject was "A General Study of Diffuse Galactic Nebulae," in which he set up a proposed classification system based on fundamental differences between galactic and non-galactic nebulae. It was also shown that these types of nebulae were made luminous by the radiation of certain stars associated with them and that the nebulosity consisted of clouds of atoms and dust, not hot enough to be self-luminous, but visible because of light from involved or neighboring stars.
Another paper, "The Source of Luminosity in Galactic Nebulae," gave the relationship of the luminosity of galactic nebulae to the magnitudes of associated stars and showed that the gases were excited and made luminous by very blue, high-temperature stars involved in or near the nebulosity
Hubble's important research work on extragalactic nebulae began at about the time when the 100-inch Hooker telescope became available for observations in 1919, and his first outstanding results were obtained in 1923 with his discovery of a Cepheid variable star in Messier 31. This discovery was highly important and significant. It was the first sure indication that M 31 was far outside the boundaries of our own galactic system. By the end of 1924, he had found 36 variable stars in M 31, 12 of which were Cepheids. Of these 12 Cepheids, Hubble found the distance of M 31 to be of the order of 285,000 parsecs
With the subsequent discovery of Cepheids in other spirals, it became possible for Hubble to calculate their distances using the same methods used to investigate the more remote regions of the galactic system. Further research showed that the relative luminosities of other stars in these systems, such as novae, irregular variables, and blue giants, corresponded reasonably well with objects like those in the Magellanic Clouds and the galactic system, and the theory of island universes was established beyond reasonable doubt.
This discovery was followed in rapid succession by papers showing that NGC 6822, Messier 33, and Messier 31 were stellar systems whose brighter stars roughly corresponded in luminosity to the same type of objects in our own galactic system.
Another large and time-consuming investigation carried out by Hubble was his survey of extragalactic nebulae to very faint limits. For this investigation
He used the 100-inch and 60-inch reflectors on Mount Wilson. Plates were centred on approximately 1,300 selected areas uniformly scattered over 75 percent of the sky. From this material, Hubble decided that the large-scale distribution of nebulae was approximately uniform except for effects of obscuration arising within the galactic system. The distribution was found to be isotropic, and as fainter limits were reached, nebulae maintained a constant rate of increase.
Hubble was the first to set up a significant classification system for extragalactic nebulae. Still used today, it was developed from the study of photographs of several thousand nebulae and was based primarily on the structural forms of photographic images. The characteristic feature of extragalactic nebulae was found to be the rotational symmetry about dominating non-stellar nuclei. The mean absolute visual magnitude derived for nebulae whose distances could be determined was found to be of the order of 15.2. Masses appeared to be of the order of 2.6 × 108 M.
Other important research results appeared in his papers on extragalactic nebulae as stellar systems, novae in nebulae, distribution of luminosity in elliptical nebulae, nebulous objects in M 31 identified as globular clusters, angular rotations of spiral nebulae, the luminosity function of nebulae, the motion of the galactic system among the nebulae, and the direction of rotation in spiral nebulae.
Many of Hubble's results were fundamental in character. His classification system for the extragalactic nebulae and the important relationship he found between redshifts and distances were of this type. His correlation between redshifts and distances, "Hubble's Law of the Redshifts," is a good example of his ability to obtain results of importance with greater available data.
In 1929, when the velocity-distance relationship was first established, the only observational data available were the velocities of some 46 extragalactic nebulae, 41 of them measured by V. M. Slipher at the Lowell Observatory, and distances of 24 objects, including the small and large Magellanic Clouds
From the 24 nebulae for which he had estimated distances, Hubble obtained his original solution, indicating that for the observed range in distance (about 6.5 million light years), velocities increased at the rate of 500 km/sec for every million parsecs of distance. Since that time (1929), measured redshifts for some 600 extragalactic nebulae have been obtained at Mount Wilson and Palomar. The largest observed redshifts now approximate one-fifth the velocity of light, and the nebulae are about 50 times more distant. It is remarkable, but typical of Hubble's work, that on the distance scale he used, the additional new data have not greatly changed his original value of the constant; the present value is about 530 km/sec per million parsecs.
Some time before Hubble's death, he had been well aware that a substantial correction to the old distance scale would eventually be necessary. The main reason for the revision was the discovery by Baade of two types of stellar populations in M 31 and the fact that Cepheids occurred in both Population I and Population II. Baade's data indicated that Cepheids of Population I are about one and one-half magnitudes brighter than the Cepheids in Population II. It now seems probable that the former calibration of the period-luminosity relation for type I Cepheids is in error by about magnitude. It follows then that M 31 is some two times farther away than Hubble's estimate, which was obtained from the type I Cepheids only. The revised distance now furnishes an explanation for a puzzling discrepancy previously noted by Hubble: namely, that the absolute magnitudes of the globular clusters in the M 31 system seemed to be from one to one and a half magnitudes fainter than those in the Galaxy. On the new distance scale they now correspond to the galactic globular clusters. Although Baade's determination of the distance of M 31 is now very close to the correct value, his factor of two cannot be used to obtain distances for the fainter nebulae, due to additional corrections arising from corrections to the apparent magnitude scale at the faint end. Sandage has already shown that the distance to M 81, for instance, is some three and one-half times the distance obtained by Hubble from the type I Cepheids. It is therefore still not possible to obtain the correct value of the Hubble expansion constant and consequently the distances to faint nebulae. In the meantime, one can say that the methods used by Hubble at the time he obtained his original solution, and thereafter, are correct and cannot be improved on today. The information he needed is still not available. Once it is, the final value of the expansion constant can be determined and distances to faint clusters of nebulae can be obtained if certain additional assumptions, such as the constancy of the absolute magnitudes, are made. It will be several years, however, before this can be done, as reliable magnitudes must be measured in many new clusters observed for velocity. When this is accomplished, the red-shift law can again be formulated and, in Hubble's own words,
In 1946, he was again free to return to astronomy. From the beginning of the 200-inch project, he had served on the Observatory Committee responsible for planning this new instrument. He now became Chairman of the Research Committee for the Mount Wilson and Palomar Observatories. Late in the fall of 1949, the 200-inch was at last available for full-time observation, and Hubble was the first to use it for observational purposes. Only an observer can understand the joy of using a great instrument, and no one was more eager than Hubble to begin work with the 200-inch. His plans were clearly laid out, and he was happy to be at work again. At the time of his death, he was preparing to go to Palomar for four nights of observing.
In addition to Hubble's long scientific bibliography, there are the Silliman Lectures at Yale, published under the title of "The Realm of the Nebulae"; and the Rhodes Memorial Lectures given at Oxford in 1936, entitled "The Observational Approach to Cosmology." He was an Honorary Fellow of Queen's College. Among other honours, he was awarded the Barnard, the Bruce and the Franklin gold medals, and the Gold Medal of the Royal Astronomical Society. He was a Trustee of the Henry E. Huntington Library and Art Gallery of San Marino, California.
In 1924 he was married to Grace Burke, and their life together was a profound and happy partnership. English, as well as American, friends will remember the hospitable welcome they always found in the Hubbles' beautiful home in San Marino and the good talk around an open fire. Hubble had many interests. He had always been a collector of books on the history and philosophy of science; he gave his valuable library to the Mount Wilson Observatory. He was a skilled dry-fly fisherman in the Rocky Mountains and on the banks of the more classic Test, near Stockbridge, where he and his wife used to stay with English friends. In fact, it was remarked by a member of the Royal Astronomical Society that it was a curious phenomenon that Hubble's lectures in the British Isles always coincided with the rise of the mayfly.
Hubble was a brilliant leader in the field of astronomy—one who will be greatly missed, not only by his close colleagues but by the astronomical world in general.
M. L. Humason
It is not easy for a close associate to evaluate in a detached manner the work of Hubble and the contributions he made toward advancing the frontiers of knowledge. But no one could be intimately associated with him without having a sincere respect for his breadth of vision, his ever-active scientific curiosity, and his confident grasp of problems
Born in Marshfield, Missouri, on November 20, 1889, Hubble was the son of John Powell and Virginia Lee James Hubble. He received his B.S. degree at the University of Chicago in 1910; was appointed Rhodes Scholar from Illinois that same year, and went into residence at Queen's College, Oxford, between 1910 and 1913, receiving his B.A. degree in Jurisprudence at Oxford in 1912. At Oxford, he had won his Blue in track events and was a heavyweight boxer, having boxed in an exhibition match with the French champion, Georges Carpentier.
In 1913, when he returned to the United States, he was admitted to the bar in Louisville, Kentucky, and for a short time practiced law successfully. He had never, however, lost his deep interest in astronomy, and at the end of a year he returned to research at the Yerkes Observatory of the University of Chicago
It may be of interest that the title of his doctoral thesis was "Photographic Investigations of Faint Nebulae." In it, he considers the possible classification of nebular types, states that the planetaries are probably within our sidereal system, while the great spirals apparently lie outside our system, and says, "These questions await their answers for instruments more powerful than those we possess." The thesis is almost prophetic of his career.
Dr. George Ellery Hale, on a visit to Yerkes, offered him an appointment on the staff of the Mount Wilson Observatory, where the 60-inch was in operation and the 100-inch was under construction. But in April 1917, the United States entered the war. Hubble, who felt that the best way to see a war was in the Infantry, enlisted immediately as a private, although it meant sitting up all night to finish his doctor's thesis and taking the oral examination the following morning. He served with the American Expeditionary Force in France as a major in command of the Second Battalion, 343rd Infantry, 86th Division. After the Armistice, he remained for an additional year of duties in Europe. In the autumn of 1919, he returned to the United States, notified Dr. Hale that he was free to accept his offer, which had remained open, and came on to Mount Wilson
A brief summary of the work accomplished by Hubble can emphasize only the highlights. His first line of research at Mount Wilson had to do with a general study of galactic nebulae. One of his papers on this subject was "A General Study of Diffuse Galactic Nebulae," in which he set up a proposed classification system based on fundamental differences between galactic and non-galactic nebulae. It was also shown that these types of nebulae were made luminous by the radiation of certain stars associated with them and that the nebulosity consisted of clouds of atoms and dust, not hot enough to be self-luminous, but visible because of light from involved or neighboring stars.
Another paper, "The Source of Luminosity in Galactic Nebulae," gave the relationship of the luminosity of galactic nebulae to the magnitudes of associated stars and showed that the gases were excited and made luminous by very blue, high-temperature stars involved in or near the nebulosity
Hubble's important research work on extragalactic nebulae began at about the time when the 100-inch Hooker telescope became available for observations in 1919, and his first outstanding results were obtained in 1923 with his discovery of a Cepheid variable star in Messier 31. This discovery was highly important and significant. It was the first sure indication that M 31 was far outside the boundaries of our own galactic system. By the end of 1924, he had found 36 variable stars in M 31, 12 of which were Cepheids. Of these 12 Cepheids, Hubble found the distance of M 31 to be of the order of 285,000 parsecs
With the subsequent discovery of Cepheids in other spirals, it became possible for Hubble to calculate their distances using the same methods used to investigate the more remote regions of the galactic system. Further research showed that the relative luminosities of other stars in these systems, such as novae, irregular variables, and blue giants, corresponded reasonably well with objects like those in the Magellanic Clouds and the galactic system, and the theory of island universes was established beyond reasonable doubt.
This discovery was followed in rapid succession by papers showing that NGC 6822, Messier 33, and Messier 31 were stellar systems whose brighter stars roughly corresponded in luminosity to the same type of objects in our own galactic system.
Another large and time-consuming investigation carried out by Hubble was his survey of extragalactic nebulae to very faint limits. For this investigation
He used the 100-inch and 60-inch reflectors on Mount Wilson. Plates were centred on approximately 1,300 selected areas uniformly scattered over 75 percent of the sky. From this material, Hubble decided that the large-scale distribution of nebulae was approximately uniform except for effects of obscuration arising within the galactic system. The distribution was found to be isotropic, and as fainter limits were reached, nebulae maintained a constant rate of increase.
Hubble was the first to set up a significant classification system for extragalactic nebulae. Still used today, it was developed from the study of photographs of several thousand nebulae and was based primarily on the structural forms of photographic images. The characteristic feature of extragalactic nebulae was found to be the rotational symmetry about dominating non-stellar nuclei. The mean absolute visual magnitude derived for nebulae whose distances could be determined was found to be of the order of 15.2. Masses appeared to be of the order of 2.6 × 108 M.
Other important research results appeared in his papers on extragalactic nebulae as stellar systems, novae in nebulae, distribution of luminosity in elliptical nebulae, nebulous objects in M 31 identified as globular clusters, angular rotations of spiral nebulae, the luminosity function of nebulae, the motion of the galactic system among the nebulae, and the direction of rotation in spiral nebulae.
Many of Hubble's results were fundamental in character. His classification system for the extragalactic nebulae and the important relationship he found between redshifts and distances were of this type. His correlation between redshifts and distances, "Hubble's Law of the Redshifts," is a good example of his ability to obtain results of importance with greater available data.
In 1929, when the velocity-distance relationship was first established, the only observational data available were the velocities of some 46 extragalactic nebulae, 41 of them measured by V. M. Slipher at the Lowell Observatory, and distances of 24 objects, including the small and large Magellanic Clouds
From the 24 nebulae for which he had estimated distances, Hubble obtained his original solution, indicating that for the observed range in distance (about 6.5 million light years), velocities increased at the rate of 500 km/sec for every million parsecs of distance. Since that time (1929), measured redshifts for some 600 extragalactic nebulae have been obtained at Mount Wilson and Palomar. The largest observed redshifts now approximate one-fifth the velocity of light, and the nebulae are about 50 times more distant. It is remarkable, but typical of Hubble's work, that on the distance scale he used, the additional new data have not greatly changed his original value of the constant; the present value is about 530 km/sec per million parsecs.
Some time before Hubble's death, he had been well aware that a substantial correction to the old distance scale would eventually be necessary. The main reason for the revision was the discovery by Baade of two types of stellar populations in M 31 and the fact that Cepheids occurred in both Population I and Population II. Baade's data indicated that Cepheids of Population I are about one and one-half magnitudes brighter than the Cepheids in Population II. It now seems probable that the former calibration of the period-luminosity relation for type I Cepheids is in error by about magnitude. It follows then that M 31 is some two times farther away than Hubble's estimate, which was obtained from the type I Cepheids only. The revised distance now furnishes an explanation for a puzzling discrepancy previously noted by Hubble: namely, that the absolute magnitudes of the globular clusters in the M 31 system seemed to be from one to one and a half magnitudes fainter than those in the Galaxy. On the new distance scale they now correspond to the galactic globular clusters. Although Baade's determination of the distance of M 31 is now very close to the correct value, his factor of two cannot be used to obtain distances for the fainter nebulae, due to additional corrections arising from corrections to the apparent magnitude scale at the faint end. Sandage has already shown that the distance to M 81, for instance, is some three and one-half times the distance obtained by Hubble from the type I Cepheids. It is therefore still not possible to obtain the correct value of the Hubble expansion constant and consequently the distances to faint nebulae. In the meantime, one can say that the methods used by Hubble at the time he obtained his original solution, and thereafter, are correct and cannot be improved on today. The information he needed is still not available. Once it is, the final value of the expansion constant can be determined and distances to faint clusters of nebulae can be obtained if certain additional assumptions, such as the constancy of the absolute magnitudes, are made. It will be several years, however, before this can be done, as reliable magnitudes must be measured in many new clusters observed for velocity. When this is accomplished, the red-shift law can again be formulated and, in Hubble's own words,
"... should furnish a clue as to the exact nature of the universe. It may then be possible to say whether or not the red-shifts are velocity shifts. If they are, then the nebulae in all directions are speeding away from us at velocities that increase directly with their distance, and space itself—the universe is expanding at a rapid rate and in a remarkable manner. And finally, it may be possible to describe the nature of the expansion and to determine the time at which the expansion began—that is, the age of the universe."
Another war, World War II, again interrupted his research. He sought to re-enter active service in the Infantry, but was prevailed upon by Army Ordnance to accept the appointment of Chief of Ballistics and Director of the Supersonic Wind Tunnel Laboratory, U.S. War Department, Aberdeen Proving Ground, Maryland. For the duration of the war, he and Mrs. Hubble remained at Aberdeen, living in a cottage on a tiny island in Chesapeake Bay. For his work here, Hubble was awarded the Medal for Merit in 1946 and continued as Consultant.
In 1946, he was again free to return to astronomy. From the beginning of the 200-inch project, he had served on the Observatory Committee responsible for planning this new instrument. He now became Chairman of the Research Committee for the Mount Wilson and Palomar Observatories. Late in the fall of 1949, the 200-inch was at last available for full-time observation, and Hubble was the first to use it for observational purposes. Only an observer can understand the joy of using a great instrument, and no one was more eager than Hubble to begin work with the 200-inch. His plans were clearly laid out, and he was happy to be at work again. At the time of his death, he was preparing to go to Palomar for four nights of observing.
In addition to Hubble's long scientific bibliography, there are the Silliman Lectures at Yale, published under the title of "The Realm of the Nebulae"; and the Rhodes Memorial Lectures given at Oxford in 1936, entitled "The Observational Approach to Cosmology." He was an Honorary Fellow of Queen's College. Among other honours, he was awarded the Barnard, the Bruce and the Franklin gold medals, and the Gold Medal of the Royal Astronomical Society. He was a Trustee of the Henry E. Huntington Library and Art Gallery of San Marino, California.
In 1924 he was married to Grace Burke, and their life together was a profound and happy partnership. English, as well as American, friends will remember the hospitable welcome they always found in the Hubbles' beautiful home in San Marino and the good talk around an open fire. Hubble had many interests. He had always been a collector of books on the history and philosophy of science; he gave his valuable library to the Mount Wilson Observatory. He was a skilled dry-fly fisherman in the Rocky Mountains and on the banks of the more classic Test, near Stockbridge, where he and his wife used to stay with English friends. In fact, it was remarked by a member of the Royal Astronomical Society that it was a curious phenomenon that Hubble's lectures in the British Isles always coincided with the rise of the mayfly.
Hubble was a brilliant leader in the field of astronomy—one who will be greatly missed, not only by his close colleagues but by the astronomical world in general.
M. L. Humason
Edwin Powell Hubble's obituary appeared in Journal of the Royal Astronomical Society 114:3 (1954), 291-295.