JSTOR

1. INTRODUCTION

Numerous accounts of Horace Babcock’s scientific accomplishments appeared in newspapers and Web sites around the world following his death on 2003 August 29. Subsequently, Arthur Vaughan (2003) prepared an excellent obituary for Horace that I cannot hope to surpass, while Allan Sandage will present Horace’s life and work in the context of a history of the Mount Wilson Observatory now nearing completion (Sandage 2004, private communication). My piece about Horace draws on much of the same source material used by my colleagues, principally his vita, bibliography, and an oral history prepared by Dr. Spencer Weart (1977) of the American Institute of Physics Center for History of Physics. The different presentations of Sandage, Vaughan, and myself reflect our different scientific perspectives and our different personal relationships with this remarkable man. A portrait of Babcock is shown in Figure 1.

(310 KB)

Fig. 1.— Horace W. Babcock, circa 1978.

Open New Window

2. EARLY YEARS

Horace Welcome Babcock’s scientific career is inextricably connected to Carnegie astronomy. It began during boyhood trips with his father, Harold Babcock, to the Mount Wilson Observatory, where he acquired lifelong interests in astrophysical phenomena and the equipment used to study them. He took this interest with him to Caltech, where, as an undergraduate, he organized a petition to initiate instruction in astronomy. Following graduation from Caltech with an engineering degree in 1934, he entered graduate school at the University of California, earning a Ph.D. at Lick Observatory in 1938 with a thesis entitled, “The Rotation of the Andromeda Nebula” (Babcock 1939). Using Nicholas Mayall’s nebular spectrograph at the prime focus of the Crossley reflector, Babcock obtained spectra along the major axis of M31 to distances of 15 from the nucleus. He also obtained spectra of four emission nebulosities previously identified by Mayall, three of which lie along extensions of the semimajor axis well outside the ordinary optical boundaries of M31. From these spectra Babcock derived the rotation curve for M31, as shown in Figure 2 (from Babcock 1939, Plate III). Upon conversion to angular velocity, he noted 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 regions.” Horace had discovered the crucial evidence for dark matter in M31 several decades before this notion gained general acceptance.

(176 KB)

Fig. 2.— Photograph of M31 with velocities plotted below (from Babcock 1939). Circles in the photograph denote locations of the emission nebulae observed by Babcock.

Open New Window

After a 1 year research assistanceship at Lick, Horace accepted a position at Yerkes/McDonald, where, at Otto Struve’s request, he designed and oversaw construction of a prime‐focus spectrograph for the McDonald Observatory 82 inch (2.1 m) telescope, which was subsequently used by Thornton Page in an important study of the interactions of double galaxies. During an instrumental foray into solar coronal measurements at McDonald, Horace made the first astronomical application of the RCA 931 photomultiplier, forerunner of the famed 1P21. World War II took him to the MIT Radiation Laboratory and thence to the Caltech Rocket Project. There he became reacquainted with Ira Bowen, director‐elect of the soon‐to‐be‐formed Mount Wilson and Palomar Observatories, whom he had first met at Lick Observatory. Bowen, recognizing Babcock’s rare combination of astronomical knowledge and optical/electronic skills, offered him a position at the Mount Wilson and Palomar Observatories, to commence 1946 January 1. There Horace was to remain for the rest of his professional career.

3. WORK AT THE MOUNT WILSON AND PALOMAR OBSERVATORIES

Horace had been hired by Bowen with the understanding that he would divide his time evenly between stellar spectroscopy and “the development of instruments using electronic techniques” (Bowen 1946). His first instrumental assignment was to construct a microdensitometer that would produce an intensity readout of the high‐resolution spectra soon to be forthcoming from the coudé spectrograph of the 200 inch (5 m) telescope. The machine fulfilled these requirements, but it was complicated, difficult to use, and Babcock regarded it as a failure. I can testify to the complexity and difficulty because guest investigator Martin Schwarzschild set me to work with it in 1951 making tracings of the spectra of high‐velocity red giants and scans of Mount Wilson solar photographs that Schwarzschild subsequently used to study the size distribution of solar granules.

In his oral history (Weart 1977), Horace remarks that early in 1946 he felt under pressure to come up with a proposal that would occupy the 50% of his time reserved for personal research. He sat down on his front porch one evening and said to himself, “I'd better come up with something here. What am I going to do in research?” He went back to fundamentals and realized that while the intensity, wavelength, and position of stellar radiation had been studied rather thoroughly, polarization had been neglected almost entirely. From that thought he drifted to Hale’s Mount Wilson investigations of solar magnetism and wondered, if “you had a star with a far stronger general magnetic field than the Sun, thousands of gauss, would there be any chance of detecting it?” He worked out the consequences of measuring the Zeeman effect produced by a dipolar field embedded in a star viewed from various directions, and he concluded that it would be worth a shot. He described a proposed “Zeeman analyzer” to Bowen, who supported the idea and promised him a couple of nights at the Mount Wilson 100 inch (2.5 m) coudé in 1946 April to try it out. His analyzer consisted of a calcite crystal followed by a suitably oriented quarter‐wave plate made of mica that he had cleaved and tested with the assistance of his father. Placed before the entrance slit of the 100 inch coudé spectrograph, it produced two stellar spectra, recorded on photographic plates, displaying left and right circularly polarized light side‐by‐side and straddled by iron arc comparison spectra. The presence of a net longitudinal magnetic field would be revealed by a systematic displacement between the oppositely circularly polarized σ components of the various doublet, triplet, and anomalous Zeeman patterns in the adjacent stellar spectra.

The rest is history. Horace found a kilogauss longitudinal field in the first star that he observed, 78 Virginis (Babcock 1947). Within 3 months he found polarity reversal on a timescale of days in a second star, HD 125248, and subsequently he found that the magnetic field of the latter varied periodically in step with previously recognized “spectrum variations” (Babcock 1951). Horace had picked the right test objects (sharp‐lined A‐type stars) for the wrong reason, a common occurrence in experimental physics. He had used an inappropriate scaling argument (the Sun was a slow rotator with a weak general field) to search for strong fields in stars that he suspected were rapid rotators viewed pole‐on. No matter. Stirred by his initial success, Horace undertook a major survey of sharp‐lined A‐type stars, which produced his famous Catalog of Magnetic Stars (Babcock 1958). For the most part he left the modeling of his discoveries to others, reasoning that his responsibility as an observer at large telescopes was to produce the primary observational data. In the course of his investigations, he explored the “Zeeman intensification” of stellar absorption lines (Babcock 1949) and discovered the “crossover effect” (Babcock 1951), which provided powerful support for Stibbs’ (1950) oblique rotator model—although Horace, to his dying day, thought otherwise, to the dismay of his admiring colleagues Armin Deutsch and George Preston. Babcock showed that among the Ap stars, magnetic field strength ranged from the lower limit of detectability with his photographic method (about 100 G in the best cases) to tens of kG in the case of HD 215441. He also discovered that indisputable magnetic fields were rare elsewhere in the H‐R diagram. The photoelectric Pockel cell polarimetry pioneered by Angel & Landstreet (1970) set new standards of elegance in the measurement of the stellar Zeeman effect, but with the exception of the extremely large magnetic fields found in degenerate stars, photoelectric polarimetry, for the most part, simply provided ever‐improved elaborations of Babcock’s pioneering investigations.

In the midst of his studies of stellar magnetism, Horace found time to think about other astronomical matters. In particular, in a 1953 PASP article (Babcock 1953a), he wrote: “In this paper a method is proposed which ‘seems to offer’ a means of compensating or correcting for the effects of atmospheric turbulence.” With these words Horace introduced the astronomical world to adaptive optics, a new discipline with powerful applications to astronomical imaging and one that will govern the design of the very large ground‐based telescopes of the future.

In this same period Babcock and his then‐retired father devised the first solar magnetograph at the Hale Solar Laboratory in Pasadena (Babcock & Babcock 1952; Babcock 1953b). An improved version of the Babcock magnetograph, installed at the 150 foot (46 m) solar tower by Robert Howard (1959), ushered in a new era of solar magnetic research. This device produces daily magnetic maps of the solar surface with high spatial resolution and sensitivity of a few gauss. Versions of this device have been used at Mount Wilson and elsewhere ever since to monitor the magnetic activity of the Sun.

Following the retirement of his father, Horace inherited responsibility for the Mount Wilson Grating Laboratory. Early on, George Ellery Hale had recognized that if he wanted high‐quality plane gratings for the spectrographs of his telescopes he would have to arrange for their construction in Pasadena, so he imported John Anderson from Johns Hopkins University to begin development of a ruling engine, assisted by Harold Babcock, another first‐generation Mount Wilson staff member. Horace assumed supervision of the lab in 1948, and following the introduction of interferometric control, the performance of the second‐generation “ruling engine” was deemed adequate for the production of high‐quality gratings with dimensions up to inches on a more‐or‐less routine basis. Subsequently, Horace supervised the manufacture of gratings, which he distributed to some 50 observatories around the world, free of charge. Work at the grating laboratory tapered off and was finally terminated as Horace entered the third phase of his career. Horace presented an excellent historical and technical review of the accomplishments of the laboratory in Vistas in Astronomy (Babcock 1986).

4. FOUNDING OF THE LAS CAMPANAS OBSERVATORY

Following World War II the rapid growth of Los Angeles greatly impaired the value of Carnegie’s Mount Wilson Observatory for work on the faint objects that were of greatest importance for advances in extragalactic astronomy and cosmology. Looking to the future, and with the endorsement of the Carnegie Trustees, Horace began site testing in 1963 for the purpose of locating a large Carnegie telescope in the southern hemisphere (the Carnegie Southern Observatory; CARSO). To identify suitable locations for such a facility, Horace invented a seeing monitor (Babcock 1963). After some exploration in Australia and New Zealand, four copies of this seeing monitor were deployed by Babcock, John Irwin, and Jurgen Stock at 10 locations in the coastal mountain ranges of northcentral Chile. Horace pursued this site testing enthusiastically because he regarded the construction of a new telescopic facility as the most attractive aspect of the Observatories directorship, which he accepted in 1964. In 1968 he finally chose Cerro Las Campanas and its environs as a site with good seeing, easily accessible from the Pan American Highway, and not too distant from a population center (La Serena/Coquimbo) that could serve as a location for administrative headquarters and provide the workforce, port facilities, and supplies necessary to maintain a mountaintop operation. When his proposal for a southern 200 inch telescope was rejected by the Ford Foundation, Horace convinced the Carnegie trustees to provide funds for a more modest facility. Following a discussion with Chilean President Eduardo Frei, he arranged for the purchase of an extensive parcel of land surrounding Las Campanas, and he negotiated an agreement with the University of Chile that guaranteed the legal security of the observatory. Henrietta Swope, a research associate of Walter Baade in Pasadena, generously provided $40,000 for the construction of an initial Perkin‐Elmer 40 inch (1.0 m) reflector. The principal facility, a 100 inch telescope, was named after Irénée du Pont, father‐in‐law of Trustee Crawford Greenewalt, who gave the initial, enabling gift of $1.5 million dollars. Ira Bowen, assisted by Arthur Vaughan, provided novel optical designs for the two telescopes, and Horace assembled a group of engineers under the supervision of Bruce Rule to design the du Pont telescope, which was built and installed at Las Campanas by L and F Industries. A road to the mountaintop was built, followed by completion of a water supply, an electrical generation facility, bodegas, and a lodge to house employees and observers. I mention these details only to remind the reader of the multiplicity of issues that Horace faced during the construction of the Las Campanas Observatory.

The 40 inch Swope reflector went into operation in 1971, and the du Pont telescope saw first light in 1976. In a tour de force of 15 years' duration, Horace had relocated the astronomical research center of the Carnegie Institution from the aged telescopes on light‐polluted Mount Wilson to new telescopes with vastly superior optical and mechanical performance located at a superb dark‐sky site that afforded access to the wonders of the southern sky—the Magellanic Clouds, the Galactic Center, and the largely unexplored South Galactic Polar Cap. When he retired in 1978 at age 65, Horace Babcock had transformed Carnegie astronomy.

Today the Las Campanas Observatory has become a multi‐institutional facility. The Japanese conduct CO surveys with their 5 m millimeter‐wave telescope; Warsaw University operates a 1.3 m telescope devoted to gravitational microlensing; the University of Birmingham investigates solar seismology with a small automated telescope; and NASA utilizes the site in its classroom instruction program. Last, and by no means least, Carnegie and its consortium partners, the University of Arizona, Harvard University, Massachusetts Institute of Technology, and the University of Michigan, jointly operate two superb 6.5 m Magellan telescopes located on Manqui, one of the peaks wisely included in Horace’s real estate purchase more than 35 years ago.

5. PERSONAL NOTES

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 National Academy (1957), the Eddington Medal of the Royal Astronomical Society (1958), the Catherine Wolfe Bruce Medal of the Astronomical Society of the Pacific (1969), the Gold Medal of the Royal Astronomical Society (1970), and the George Ellery Hale Prize of the Solar Physics Division of the American Astronomical Society (1992). Although he seemed indifferent to the honors bestowed upon him, he was fiercely proud of his inventions, the microdensitometer not included, and he lamented in his oral history that he simply did not have enough time to develop a number of devices and procedures that he had conceptualized during his career.

As a younger man, Horace shared an enthusiasm for ham radio with Olin Wilson, whom he first met at Mount Wilson in the mid 1930s. When Horace took a position at Yerkes Observatory, the two young men communicated between Williams Bay and Pasadena for fun with homemade CW equipment. Later in life Horace relaxed at sea on a 26 foot sailboat that he kept in a slip at Redondo Beach. On two occasions he invited Arthur Vaughan, James Westphal (a fellow sailor), and me to accompany him on weekend voyages, one to the Catalina Isthmus, and another in an abortive attempt to find tiny Santa Barbara Island at night.

Horace was a reserved man who seemed to measure his words on all occasions. He was ill at ease in public situations, and attempts at humor frequently sailed right over his head, as when Robert Howard proposed during an Observatory Committee meeting that we rename ourselves Carwash. He was steadfast, even obdurate, in the execution of his plans to create a Las Campanas Observatory, and he could become quite prickly when confronted with unwelcome opinions or advice. However, he never bore malice and treated all who knew him with respect.

Horace is survived by a daughter, Ann L. Babcock, and son, Bruce H. Babcock, by a first marriage, and a son, Kenneth L. Babcock, by a second marriage to Elizabeth Aubrey (divorced), who survives him.