Photograph by Mount Wilson and Los Campanas Observatories

Photograph by Mount Wilson and Los Campanas Observatories



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Photograph by Mount Wilson and Los Campanas Observatories

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HORACE WELCOME BABCOCK September 13, 1912−August 29, 2003 By GEORGE W. PRESTON H orace babcock’s career at the Mount Wilson and Palomar (later, Hale) Observatories spanned more than three decades. During the first 18 years, from 1946 to 1964, he pioneered the measurement of magnetic fields in stars more massive than the sun, produced a famously successful model of the 22-year cycle of solar activity, and invented important instruments and techniques that are employed throughout the world to this day. Upon assuming the directorship of the observatories, he devoted his last 14 years to creating one of the world’s premier astronomical observatories at Las Campanas in the foothills of the Chilean Andes. CHILDHOOD AND EDUCATION Horace Babcock was born in Pasadena, California, the only child of Harold and Mary Babcock. Harold met Horace’s mother, Mary Henderson, in Berkeley during his student days at the College of Electrical Engineering, University of California. After brief appointments as a laboratory assis- tant at the National Bureau of Standards in 1906 and as a physics teacher at the University of California, Berkeley, in 1907, Horace’s father was invited by George Ellery Hale in 1908 to join the staff of the Mount Wilson Observatory (MWO), where he remained for the rest of his career. (Harold 17

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18 BIOGRAPHICAL MEMOIRS Babcock was elected to the National Academy of Sciences in 1933.) In 1912, when Horace was born, the Mount Wilson Obser- vatory was in its heyday of expansion. The newly completed 60-inch telescope, then the largest in the world, was to be eclipsed within the decade by the 100-inch Hooker telescope under construction nearby. Thus, Horace Babcock, son of a Mount Wilson astrono- mer, grew up in the environment of a great observatory in the making. In his oral interview for the American Institute of Physics (AIP) Horace recalls that many of his childhood recollections relate to Mount Wilson, seeing the astronomers, being aware of construction on the mountain, in particular “the noisy riveting of the 100-inch dome. . . So it was only natural that I would have an early strong interest in astron- omy.” Horace, attracted to science, went to the Pasadena public grade and high schools. For understandable reasons he was also interested in engineering, so much so that he majored in structural engineering at Caltech, and it was only after he graduated in 1934 that he decided to go into astronomy. Thr oughout his life Horace was fascinated by fine mechanisms and by electrical and optical instruments. His father cultivated these interests by involving Horace in his own work from childhood. But, Horace remarks in his AIP oral interview, his father was careful never to try to make major decisions for him. Rather he tried to show Horace where opportunities and interests might lie. For example, he introduced Horace to photography and helped Horace build a 6-inch telescope. In 1928 Horace, then 16 years old, spent six weeks as a volunteer in the MWO optical shop, where he learned how to make lenses, mirrors, and prisms. During the summers of 1930, 1932, and 1935 he worked as a volunteer observer with the Snow solar telescope and

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19 HORACE WELCOME BABCOCK 150-foot solar tower on Mount Wilson, where he produced spectrograms of the solar chromosphere, especially in the infrared. He published five short papers about these activi- ties in the Publications of the Astronomical Society of the Pacific (one with his father). This was a period of learning outside the conventional paths of public education. He was learning practical spectroscopy, measuring wavelengths, and acquir- ing familiarity with the reference materials of observational astrophysics. In the course of these adventures he inevitably became acquainted with many astronomers at Monastery mealtimes. “The Monastery” was the official name of the (at that time all-male) sleeping and eating facility for observers on the observatory grounds. In the spring of 1930 Horace accompanied an MWO party that included his father, Seth Nicholson, and Ted Dunham to observe a total solar eclipse in Nevada. In 1930 Horace also began his undergraduate studies at Caltech, a personal goal since childhood. He was well aware that the design and assembly of a 200-inch telescope were under way there. He majored in engineering (as his father did in Berkeley), but also studied physics (electricity and light, which he liked best). There was no undergraduate astronomy course at Caltech at that time. Horace wanted to study astronomy, so he wrote a petition asking that such a course be taught and posted it on a campus bulletin board. Many students signed it, and the next year such a course was offered by physicist John Anderson, head of the 200-inch telescope project under Hale. Horace was pleased to think that his petition had played a role in this development. By 1934, when he graduated from Caltech, Horace knew that he wanted to be an astronomer. He realized that he would need a Ph.D., unlike his father who had gone to work at MWO with only a B.S., and Walter Adams, the director,

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20 BIOGRAPHICAL MEMOIRS who had only an M.S. Horace hoped that when the 200-inch telescope went into operation (then expected to happen around 1938) he might have a chance to participate in its use. Horace had visited Palomar Mountain before anything had been built there, and he was taken by the challenge of locating the 200-inch in that primitive environment. The graduate school that most closely aligned with Horace’s interests was the University of California, meaning course work in Berkeley and thesis work at the Lick Observa- tory on Mount Hamilton in California. “I didn’t have much inclination to think of going to an Eastern university, which would not be strong on observing anyway. The University of California had the Lick Observatory and it was the place to go.” Horace did not have a scholarship or assistantship during his three years on the Berkeley campus; his father paid his expenses. Horace’s uncle, Ernest B. Babcock was a biology professor at Berkeley (also elected to the National Academy of Sciences, in 1946). It is possible that Horace lived with his family there. Horace found the Berkeley Astronomy Department to be quite old-fashioned (“post-mature” to use the euphemism in his oral interview). It was dominated by several big names in “theoretical astronomy,” a term which at that time in Berkeley meant “orbit theory.” Horace had already been exposed to the new astrophysics that Hale had made the centerpiece of research at the Mount Wilson Observatory, but only Donald Shane, subsequently director of Lick Observatory, taught astrophysics at Berkeley in 1935. However, there were good physics courses. Horace enjoyed those offered by Robert Birge, Francis Jenkins, Harvey White, and particularly by J. R. Oppenheimer, whom Babcock regarded as remarkably articulate. Of course, there was the attraction of the Lick Observatory. While in Berkeley, Horace became acquainted with Nicholas Mayall of Lick Observatory, under whom he

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21 HORACE WELCOME BABCOCK would later pursue his thesis observational work. Babcock regarded Mayall’s extragalactic research with his nebular spectrograph at Lick’s Crossley telescope as a “shining ex- ample of achievement.” Horace credits Mayall for proposing measurement of the rotation of the galaxy M31 (Andromeda Nebula) as a Ph.D. thesis topic. Mayall also provided a spectrograph at the 36- inch Crossley reflector capable of making the measurements, and he offered suggestions about places to make observa- tions in the outskirts of M31, faint emission wisps. Horace took up these suggestions in his fourth year of graduate work, now supported by a fellowship, on Mount Hamilton. Most of his spectra were obtained with a long slit placed along the major axis of the galaxy. Velocities in the inner regions with sufficient surface brightness were derived from wavelength displacements of absorption lines produced by myriads of unresolved stars. Additionally, he observed five faint nebulosities identified by Mayall in the outer reaches of M31, where starlight is too weak to measure. We now recognize these wisps as H II regions similar to the Orion Nebula located nearby in our Milky Way Galaxy. They could provide velocities because they shine brightly at a relatively few discrete wavelengths due to the fluorescence of gas clouds illuminated by hot stars. The work was arduous. Ex- posure times were long, 10 to 20 hours (several nights spent obtaining each spectral photograph), but the results were spectacular. They are displayed in his thesis, published as Lick Observatory Bulletin, No. 498 in October 1939 and now reproduced in a more readily available journal Publications of the Astronomical Society of the Pacific, volume 116. The rotation curve produced by this work (a plot of line-of-sight velocity derived from the optical Doppler effect versus angular position along the major axis of the galaxy)

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22 BIOGRAPHICAL MEMOIRS did not decline outside the galaxy’s luminous bulk. Rather, it continued to rise to the outer angular limits of Horace’s observations. This behavior was contrary to the expecta- tions for Keplerian motion about a central gravitating body (in which velocity decreases inversely as the square root of distance from the center of the system). He analyzed the velocities, advised by Lick astronomer R. J. Trumpler, and found that they did not match the rotation curve calculated for the constant mass-to-light ratio, then the usual assump- tion made for starlight. Upon converting his radial velocities to angular velocities about the center of M31, Horace noted in his thesis that “the obvious interpretation of the nearly constant angular velocity from a radius of 20 minutes of arc outward is that a very great proportion of the mass of the nebula must lie in the outer (dim) regions.” In retrospect we now know that Horace had come upon the crucial evi- dence for the existence of dark matter, but like Wegener’s continental drift, it was a discovery before its time. No one could make any sense of it. He completed writing his thesis by June 1938 and got his Ph.D. W. H. Wright, the Lick director, arranged for Horace to make oral presentations about his M31 rotation curve at the 1939 annual meeting of the American Philosophical Society (APS) in Philadelphia and at the dedication of the brand- new McDonald Observatory in Texas immediately afterwards. His paper fit right into the subject of the APS symposium, “Structure and Dynamics of Galaxies,” and he discussed it afterward with Bertil Lindblad and Jan Oort, two of the world experts who gave review papers there. Babcock’s was the first published rotation curve that extended significantly beyond the bright nuclear bulge of M31 into the spiral arm regions of the galaxy. Everyone agreed that his results were important, but no one had a good explanation for them. Thus, Horace’s graduate education concluded on a satisfac-

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23 HORACE WELCOME BABCOCK tory though puzzling note; at the least he had attracted some attention. Shortly thereafter Otto Struve offered him a posi- tion at yerkes and McDonald Observatories. Horace believed that his presentation at McDonald got him the job. GETTING STARTED Before going to yerkes, Horace enjoyed the summer of 1939 as a postdoc at Palomar working on a project partly financed by 200-inch funds. He used a small spectrograph put together around a fast Schmidt camera and a grating provided by his father, who was in charge of the MWO grat- ing laboratory at that time. He and Josef Johnson, a gradu- ate student working with Caltech astrophysicist Fritz Zwicky, took spectra of the night sky, which they continued through the year. Their system was responsive well into the UV, and it showed many night-sky bands in that region, which we now know are mostly emitted by various excited levels of terrestrial, atmospheric molecular oxygen (O2). They also tried to trace the night-sky brightness variations through the night and through the year, but it was too complicated to unravel. One of their conclusions: “For the photography of faint nebulae it would seem advantageous to filter out the ultraviolet light.” Perhaps because of their UV observations, the Palomar high command decided not to try to include that spectral region in the Palomar Sky Survey to be conducted by the 48-inch Schmidt telescope. Consequently, the Schmidt corrector plate was made of plate glass (to block the UV) rather than from UV transmitting glass. This design feature would increase the limiting magnitude of the blue exposures, an important improvement. Babcock, living at Palomar that summer of 1939, was one of the first astronomers to make an extended stay in the Lodge, as it was then called. He liked it and hoped to get a staff job there, but the 200-inch

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24 BIOGRAPHICAL MEMOIRS was being put on hold because of World War II, and was far from complete. MCDONALD AND yERKES OBSERVATORIES Otto Struve, director of yerkes and McDonald Observa- tories by agreement between the University of Chicago and the University of Texas, was eager to hire young astronomers trained at other top observatories to work at McDonald. Wright’s recommendations played a significant role in Struve’s choices of Horace and his fellow Berkeley graduate student Daniel Popper, according to Osterbrock (at the 2004 Bab- cock Memorial Symposium). The positions were attractive, because the new 82-inch reflector was then the second largest telescope in the world. Horace would have preferred a job at Mount Wilson Observatory, but his father and Director Walter S. Adams, a close friend of the family, told him the experience would be useful to him in the long run. Horace, by virtue of his thesis experience, was very in- terested in nebular spectroscopy, but even the fastest spec- trograph of the 82-inch, used at the Cassegrain, was far too slow. Instead he had to work on low-resolution spectroscopy of relatively nearby bright stars, collaborating with other astronomers on their programs. One was with Popper on nova-like variables; another, with Philip Keenan, was devoted to spectra of stars near the north galactic pole. Struve asked Horace to design a fast nebular spectro- graph to be used at the prime focus, a concept Frank Ross, then a senior yerkes staff member, had suggested to him. Horace had little experience in designing instruments, but his engineering training at Caltech and his discussions with his father had prepared him admirably for the task. He designed a grating spectrograph (unusual because good gratings were rare); his father, now supervisor of the Mount Wilson grating laboratory, was able to provide one for him.

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25 HORACE WELCOME BABCOCK It was pierced, so it could be used with a parabolic mirror collimator on axis, the favored MWO design at the time. There was no instrument maker at McDonald, so Horace had to make the drawings and send them back to Williams Bay, where yerkes machinist Charles Ridell constructed the mechanical parts. George Van Biesbroeck, the astronomer in charge of the shop, modified the plans, probably to simplify the work, before handing them over to Ridell, and neither Van Biesbroeck nor Struve felt called upon to notify Horace of the changes. He learned of them only when the parts arrived at the remote McDonald observing site, where the instrument could not be assembled and used effectively. Horace, who had been counting on using the spectrograph, wrote a hot letter to Struve asking why he had not been con- sulted, and Struve replied at once, chastising him severely for daring to question the judgment of his elders. In fact both of his elders were quite out of date about spectrographs, as demonstrated by the other instruments at McDonald, but as a result Horace did not manage to do nebular spectroscopy there. In spite of this early confrontation Horace expressed admiration for Struve’s research and management style at the yerkes-McDonald enterprise. After World War II, Horace’s fast B spectrograph was slightly modified by Thornton Page, who used it to measure the velocity differences in pairs of galaxies. The result Page found, that the indicated masses of the individual galaxies were larger than expected, was another manifestation of dark matter, not understood by Page or anyone else at that time. After Page left Chicago, the B spectrograph was used by Margaret and Geoffrey Burbidge to measure rotation curves of numerous other nearly edge-on galaxies. Thus, Horace’s instrumental efforts at McDonald enabled important later extensions of his thesis work at Lick.

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26 BIOGRAPHICAL MEMOIRS Soon after completion of the spectrograph in 1941 Struve asked him to take on the coronaviser, a device on loan from Bell Telephone Laboratories that had been invented by A. M. Skellet for observation of the solar corona outside of eclipse. Among improvements made by Babcock was use of an RCA 931, the first astronomical application of this precursor of the famed 1P21 photomultiplier. Within the year, Horace was rotated from McDonald back to yerkes for a long stay and a chance to write up his results. There he had many discussions with S. Chandrasekhar, then working in stellar dynamics, about the M31 rotation curve. Horace liked Chandra and enjoyed hearing his talks, but he wrote that the acclaimed theorist didn’t understand much about observational astronomy. While at yerkes, Horace met, wooed, and married Marga- ret Anderson, an eighth-grade school teacher at Williams Bay High School. Later that year the two went back to McDonald, but the year was 1941 and America was close to entering World War II. Scientists were in demand for weapons projects, especially experimental physicists with skills in electronics. Albert Whitford had been recruited to the MIT Radiation Lab to work on radar in 1940; he had recruited Gerald Kron to come there, too, and now Kron recruited Horace, who arranged with Struve to take an indefinite leave of absence. He and his wife drove across the country (after a visit to his parents’ home in Altadena), with perhaps a stop at the last big prewar American Astronomical Society meeting at yerkes (in September 1941), and then on to Cambridge. WORLD WAR II Horace arrived in Cambridge knowing little more than that the Radiation Laboratory was engaged in electronics. Security was surprisingly tight and he was given to feel that

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43 HORACE WELCOME BABCOCK telescope would not be forthcoming soon, if ever. Horace was not deterred. In 1966 while all this was playing out, Bowen received the prestigious George Darwin Award of the Royal Astronomical Society, and in October delivered his George Darwin lecture titled Future Tools of the Astronomer, in which he opined that survey telescopes with large fields of view would be impor- tant for the future of observational astronomy. At Horace’s urging Bowen began to think about a survey telescope for the Carnegie Southern Observatory. His ideas later evolved into the 40-inch and 100-inch telescopes that were actually built. A pivotal meeting of the Carnegie staff was held at Carnegie’s Santa Barbara Street offices on June 7, 1966. The attendees were Robert Kraft, Olin Wilson, Armin Deutsch, Allan Sandage, Henrietta Swope, and Arthur Vaughan, with Horace chairing the meeting. Horace explained to the staff that Carnegie trustees had earmarked $2 million for a joint Carnegie-Caltech astronomy building on the Caltech campus, but that if a decision could be reached to proceed with a southern observatory, the institution might have a serious problem in providing its share of the funding. Horace polled the staff and reported to Ackerman: “The Observatory staff is firmly of the opinion that, if necessary, construction of a new headquarters building in Pasadena should be postponed in order to assure funding of the CARSO (Carnegie South- ern Observatory) project.” Furthermore, “If construction of a 200-inch proves impossible in the near future, we should … make an early beginning with the largest and best instru- ment that can be built with available funds… Bowen’s design for a wide-field 85-inch telescope should be explored.” This expression of priorities by the Carnegie staff dealt a mortal blow to plans for a new astronomy building at Caltech, and was received with dismay by campus astronomers.

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44 BIOGRAPHICAL MEMOIRS The negotiations with officials of AURA for a Carnegie observatory site at Cerro Morado dragged on for some two years after funding for a Carnegie 200-inch had failed to materialize. AURA’s position was that the Morado site would remain under AURA ownership but leased to Carnegie, and the lease would be limited to an area of some 92 acres, far too small to accommodate the array of large telescopes Horace envisioned. Horace washed his hands of that option. Meanwhile the site survey work continued. Babcock and John Irwin, who ran the site testing program in Chile, summarized their conclusions in an unpublished memoran- dum: In 1968 it became clear that Las Campanas came closer than any other site in meeting the prescribed CARSO criteria: 29 degree S latitude; 7500-8300 feet elevation, with ample space for many telescopes; only 40 miles from the coast and well-separated from the cordillera; good topography, with no mountains to windward; no prospect of future light pollution; easy road construction; ready availability for purchase; and, as confirmed by test wells, adequate water sources. In September 1968 Horace wrote to Ackerman that in view of the lack of substantial progress in his attempts to deal with AURA, he [Babcock] proposed informally that Carnegie should promptly review the possibility of locating on Las Campanas instead of Morado. This proposal was ap- proved, and Morado was abandoned. On November 19, 1968, Horace met with Eduardo Frei, the President of Chile, in Santiago and received approval to purchase Las Campanas. President Frei said that he was strongly interested in the project and that it had his cordial support. . . He inquired whether Horace was having any par- ticular difficulties in our negotiations and, following some discussion, Frei telephoned the minister of land requesting that he give Horace all possible assistance. At meeting’s end President Frei assured Horace, “The land is yours.” It is a big

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45 HORACE WELCOME BABCOCK piece of land (50,000 acres, 84 square miles at purchased price for about 30 cents an acre. Not all of that area is suit- able for supporting telescopes, but choice sites for additional telescopes lie along a long ridge extending from Cerro Las Campanas northward past Cerro Manqui, site of the Magellan Telescopes, to Cerro Manquis, where the du Pont Telescope is located. The surrounding land area affords a generous buffer against future sources of interference. Shirley Cohen’s interview of Caltech’s James Westphal (at website http://oralhistories.library.caltech.edu/107/01/ OHO_Westphal_J.pdf, particularly pp. 71-74) contains a fascinating alternative account of some events that preceded purchase of the Las Campanas property. Horace had en- listed the assistance of Westphal, whom I can best describe as Caltech’s 20th-century Renaissance man because of his broad laboratory and field experience, and his facility in matters of engineering, electronics, and astronomy. With the purchase of the Las Campanas property, Hor- ace had the land but not the funds to develop it or to build telescopes. Among Horace’s papers Vaughan found a hand- written note dated April 13, 1970: “Dr. Haskins telephoned me today to say that . . . the (du Pont) family is seriously con- sidering closing out one of its foundations. . . Dr. Greenewalt would like to see the assets go to the Southern Observatory.” Crawford Greenewalt was at that time president of E. I. du Pont de Nemours and Co., and his wife, Margarita, was the daughter of the late company president and chairman Irénée du Pont. The upshot of all this was that Horace Babcock and Allan Sandage met with Mrs. Greenewalt at Carnegie headquarters in Washington to answer questions she posed. The conversation must have been productive, because the Greenewalts donated $1.5 million toward the construction of “a 60-inch or larger telescope, the balance of its cost to be provided by the Carnegie Institution.” In December 1970

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46 BIOGRAPHICAL MEMOIRS the trustees authorized the construction at Las Campanas of a 100-inch telescope, to be named after Mrs. Greenewalt’s father. After seven years of traveling, testing, and talking, Horace aided by only a few close associates had finally set Las Campanas Observatory on its course. Soon thereafter, Horace created the Las Campanas Ob- servatory Committee, which included Bruce Rule as chief engineer, Ed Dennison in charge of electronics, J. B. Oke (Caltech) responsible for auxiliary instruments, Art Vaughan responsible for optics, and Bruce Adkison responsible for administration in Chile, with Ira Bowen serving as consultant. Horace chaired the committee. The first meeting was held on January 20, 1971. Horace’s notes documenting the 36 or so Las Campanas Observatory Committee meetings held over the next five years (through January 1976) provide a detailed record of the course of the project. Site development at Las Campanas proceeded under increasingly difficult conditions. Chile in the 1970s was wracked by severe inflation, political tensions, strikes, and other disruptions, including the assassination of Salvador Allende in Santiago in 1973. Schedule delays and cost over- runs brought Horace into conflict with increasingly grumpy officials of the Carnegie Institution of Washington. Through all of these vicissitudes Horace endeavored to keep the scientists on his staff informed about the status of the Las Campanas Project, while protecting their freedom to remain focused on research. For the most part the scientists paid little attention to the project, until shortly before the du Pont telescope was to be dedicated in late 1976, when the impact of having to staff and operate a new observatory could not be ignored. The Swope 1.0-meter and du Pont 2.5-meter telescopes built in the 1970s were only the first steps in the development of the major observatory Horace Babcock had envisioned

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47 HORACE WELCOME BABCOCK when he became director in 1964. Thanks to the continuing efforts of succeeding generations of Carnegie astronomers following in Horace’s footsteps, Las Campanas is now the site of the two superbly engineered 6.5-meter Magellan telescopes, operated by a consortium consisting of Carnegie Institution of Washington, University of Arizona, Harvard University, Massachusetts Institute of Technology, and University of Michigan. And with installation of the Polish 1.2-meter OGLE (Optical Gravitational Lensing Experiment) telescope and the University of Birmingham (U.K.) automated solar oscil- lation telescope, the Las Campanas operation has taken on an international flavor. Horace enjoyed the opportunities that came his way for interacting with folks at the working level in the Las Campa- nas Project. He spoke their language. They appreciated his encouragement. The Las Campanas Observatory that grew out of Horace’s vision represents a supreme asset in the hands of the astronomers who use it today. Its value lies not only in the quality of its dark skies and exquisite seeing but also in its infrastructure, including roads, water resources, and geographical expanse suitable for accommodating the largest telescopes currently foreseen. This asset is Horace’s legacy, for which he deserves lasting recognition and thanks. Horace’s efforts at Las Campanas perturbed relations among astronomers in Pasadena in several ways. First, the decision to create Las Campanas Observatory was viewed with dismay by some Caltech astronomers, most notably by Jesse Greenstein, who worried that the new facility would put Carnegie and Caltech into a competition for founda- tion money in which both institutions would lose. Jesse would have preferred to see the Carnegie Institution invest its astronomical resources at Palomar Observatory, so that it could better compete with well-funded national (AURA) and international (ESO) facilities. Furthermore, the relatively

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48 BIOGRAPHICAL MEMOIRS modest aperture of the 100-inch du Pont telescope did little to redress the imbalance between Carnegie and Caltech facili- ties. Beyond that, I believe there was a general perception among Caltech astronomers in the 1970s that Babcock was primarily a Carnegie director, who devoted far too much of his effort to Las Campanas, and virtually none to fund raising and scientific administration for the improvement of Palomar. Such feelings began to erode the collegial founda- tions of the joint operation of Hale Observatories. Worries about this erosion, in turn, created concern among some Carnegie astronomers, who feared that collapse of the Hale Observatories would endanger their access to the 200-inch telescope. Such issues may have bothered Horace as well, but they did not weaken his resolve to complete Las Campanas Observatory. Thirty years later these concerns are largely forgotten, indeed unknown to the present generation of astronomers, but they seemed very important in 1975, and they should be acknowledged in considering the impact of Horace Babcock’s drive to create Las Campanas Observa- tory. CODA Horace Babcock seldom looked back. He labored long and hard to establish superb empirical foundations of sub- jects that he had mastered—stellar and solar magnetism—but he never again published a refereed paper on these topics after accepting the observatories directorship in 1964. He worked tirelessly to initiate and oversee completion of Las Campanas Observatory: the infrastructure (access roads, water supply, electrical system, lodge) and the telescopes (1.0-meter Swope and 2.5-meter du Pont), but he never set foot on the mountain after his retirement in 1978. He de- voted his postretirement years almost exclusively to topics in

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49 HORACE WELCOME BABCOCK experimental instrumentation: optical gyroscopes, adaptive optics, a pneumatic telescope. Such devices were perhaps his first love, and he returned to them. Horace won worldwide acclaim for his contributions to astronomy. Following his election to the National Academy of Sciences in 1954, he was the recipient of the Henry Draper Medal of the Academy in 1957, the Eddington Medal of the Royal Astronomical Society in 1958, the Catherine Wolfe Bruce Medal of the Astronomical Society of the Pacific in 1969, the Gold Medal of the Royal Astronomical Society in 1970, and the George Ellery Hale Medal of the Solar Physics Division of the American Astronomical Society in 1992. In 2004 Symposium No. 224 of the International Astronomical Union, titled “The A Star Puzzle,” convened in Poprad, Slo- vakia. A session held on the first evening of the symposium was devoted to memorial presentations about Vera Khoklova, a Russian astrophysicist who died in 2003, and about Horace Babcock. Horace was a reserved man who seemed to measure his words on most occasions. He was ill at ease in public situa- tions. He was steadfast, even obdurate, in the execution of his plans for Las Campanas. On the lighter side, Horace en- joyed the sea, and from time to time he relaxed on a 26-foot sailboat that he kept in a slip at Redondo Beach, California. On more than one occasion he invited Pasadena astronomers to accompany him on weekend excursions to the Channel Islands. As one might expect, his boat was equipped with an autopilot of his own design. And, of course, the autopilot took its directions from the earth’s magnetic field. Following retirement Horace continued to work quietly in his office at Santa Barbara Street until 1998, when he moved to a retirement community in Santa Barbara to be near a son. He died 15 days short of his 91st birthday in 2003 and

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50 BIOGRAPHICAL MEMOIRS was buried in the family plot at Mountain View Cemetery in Pasadena, following a simple graveside gathering of family and friends, at which his children in turn reminisced about their father. Horace is survived by his children: Ann L. and Bruce H. by his first marriage, and Kenneth L. by a second marriage, to Elizabeth Aubrey (divorced). in p reparing t his m emoir I b orrowed from presentations of Donald Osterbrock and Arthur Vaughan delivered at the Babcock Memorial Symposium held at Caltech on May 21, 2004. I also referred exten- sively to the American Institute of Physics oral interview of Horace conducted by Spencer Weart on July 25, 1977. Some of my remarks are based on personal recollections.

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51 HORACE WELCOME BABCOCK SELECTED BIBLIOGRAPHy 1939 The rotation of the Andromeda Nebula (Ph. D. thesis). Lick Obs. Bull. No. 498. 1947 Zeeman effect in stellar spectra. Astrophys. J. 105:105-119. 1948 A photoelectric guider for astronomical telescopes. A strophys. J. 107:73-77. 1949 Magnetic intensification of absorption lines. Astrophys. J. 110:126- 142. Stellar magnetic fields and rotation. Observatory 69:191-192. 1951 The magnetically variable star HD 125248. Astrophys. J. 114:1-35. 1952 With H. D. Babcock. Mapping the magnetic fields of the sun. Publ. Astron. Soc. Pac. 64:282-287. 1953 The possibility of compensating astronomical seeing. Publ. Astron. Soc. Pac. 65:229-236. 1955 With H. D. Babcock. The sun’s magnetic field, 1952-1954. Astrophys. J. 121:349-366. 1958 A catalog of magnetic stars. Astrophys. J. 3(suppl.):141-210. Magnetic fields of the A-type stars. Astrophys. J. 128:228-258.

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52 BIOGRAPHICAL MEMOIRS 1961 The topology of the sun’s magnetic field and the 22-year cycle. As- trophys. J. 133:572-586. 1963 Instrumental recording of astronomical seeing. Publ. Astron. Soc. Pac. 75:1-8. The sun’s magnetic field. Annu. Rev. Astron. Astrophys. 1:41-58. 1977 First tests of the Iréneé du Pont telescope. Sky Telescope 54:90. 1986 Diffraction gratings at the Mount Wilson Observatory. Vistas Astron. 29:153-174.

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53 HORACE WELCOME BABCOCK