Arthur Edward Lilley
The 21-cm wavelength line of neutral hydrogen (HI) had been discovered in the interstellar medium (ISM) by Ewen and Purcell in the spring of 1951, using a receiving system pointed south from the fourth floor of Harvard's Lyman Laboratory. Professor Bart Bok in the Astronomy Department responded enthusiastically and started a program to study the galactic distribution of HI. Ed and David Heeschen were the first graduate students in the program, which eventually produced nine PhD theses under the supervision of Bok.1 They helped assemble and commission a 24-ft parabolic antenna equipped with a single channel radiometer, at a site in Harvard, Massachusetts. Ed defended his thesis entitled, “A Radio Study of the Association of Gas and Dust,” in November 1954. He had been at Harvard for just over three years. In his thesis, he made the first empirical measurements of the gas-to-dust ratio in interstellar space and derived a value that still remains the standard value now, some 65 years later. His paper on the thesis was published in the Astrophysical Journal in 1955 and has been widely cited. Although radio astronomy began in 1932, Ed and Dave Heeschen were the first to earn PhDs in the field in a US department of astronomy.
He took a position at the Naval Research Laboratory (NRL) in the prominent radio group under John Hagen. There he helped initiate a 21-cm HI program. His most significant result was a study of absorption towards the supernova Cassiopeia A. From the galactic rotation model, he was able to show that Cass A was much more distant than thought at that time. In 1956 he worked with Alan Barrett to search for interstellar OH. They were not successful, primarily because the transition frequency was not accurately known. In 1958 he joined the faculty at Yale, but moved to Harvard in 1959 where he led the program in radio astronomy, which included directing the Agassiz Station’s 60-ft radio telescope in Harvard, Massachusetts, that had been commissioned in 1956. He received tenure in 1963. In 1968 he oversaw the replacement of the 60-ft reflector of the Agassiz telescope with a surplus 84-ft reflector on the existing mount. This upgrade doubled its collecting area.
Ed was the co-PI, along with Alan Barrett, for the microwave radiometer instrument on the Mariner II spacecraft in 1962, NASA’s first successful planetary mission. The spacecraft made high resolution scans of Venus during its flyby and showed that the radio emission at 1.3 and 1.9 cm wavelength was limb-darkened. This supported the primary theoretical model of the time that Venus had a hot surface (600K) and a cooler and very dense molecular atmosphere of 250K.
Both radio recombination lines and OH maser emission in the ISM were detected in 1965. Lilley, with his graduate students, Pat Palmer and Ben Zuckerman, began studying both. They made the first detection of recombination lines from helium and carbon, and made the first detection of OH maser emission in an excited rotational transition (2Π1/2, J=1/2). This was the first detection of a radio line from a molecule formed in the ISM from energy levels above the ground state.
Ed spent much of his effort in the period 1963 to 1972 designing and promoting a 440-ft radio telescope for general use in radio and radar astronomy at centimeter wavelengths. Inspired by the Haystack telescope, it was to be enclosed in a radome. The project began as a collaboration between MIT and Harvard as the Cambridge Radio Observatory Committee (CAMROC), was broadened to a regional facility named the New England Radio Observatory Corporation (NEROC), and culminated in the submission of a bill for a national facility on the floor of Congress by the Smithsonian Institution (with a funding stream outside of the NSF). Lilley was the executive director and Board member of NEROC. The 1960s was a period of growth and competition in the radio astronomy community. In addition to a large monolithic telescope, there were designs for interferometric arrays by the National Radio Astronomy Observatory (NRAO), Caltech and Stanford. Two separate ad hoc committees chaired by Robert Dicke tried to establish priority among the various initiatives. It became clear that the community would receive backing for only one major project and support coalesced behind the Very Large Array (VLA) of NRAO. It was ranked the top priority in the radio panel and the main committee of the 1970s NAS Decadal Survey led by Jesse Greenstein. It was funded by the NSF and dedicated in 1980. The US finally constructed a fully steerable telescope of the size class of the NEROC telescope, the 100-m NRAO Robert C. Byrd Green Bank Telescope, which was commissioned in 1994, two years before he retired. This saga has been extensively reported.2
In the early 1970s Ed obtained support from both Harvard and the colocated Smithsonian Astrophysical Observatory (SAO) to establish a research group focused on the emerging field of astrochemistry.3 The group he assembled consisted of John Ball and Dale Dickinson (observations), Carl Gottlieb and Harry Radford (laboratory spectroscopy and observations), Marvin Litvak (theory), Jim Moran (molecular masers) and Hayes Penfield (instrumentation). He helped to found the collaboration among Harvard, the University of Texas (UT), Goddard Institute of Space Studies, and Bell Laboratories to instrument and use the 5-m millimeter-wavelength telescope (MWT) of UT on Mt. Locke Texas. Using the MWT, the NRAO 140-ft and the NRAO Kitt Peak 36-ft telescopes Lilley’s group made the first detections of interstellar formic acid (H2CO2), methyl alcohol (CH3OH), trans-ethyl alcohol (CH3CH2OH)4, ethyl cyanide (CH3CH2CN), nitrogen sulfide (NS), sulfuric oxide (SO) and acetaldehyde (CH3CHO). The group also did extensive studies of other molecules, such as HCN, in molecular clouds.
Ed was also interested in the characteristics of the earth’s atmosphere. He wrote a paper with Litt Meeks in 1962 concerning atmospheric oxygen lines at 60 GHz. In the late 1970s Ed and colleagues built a special purpose radiometer to study the water vapor and ozone in the earth’s mesosphere.
From 1982 to 1994, Ed supervised the operation of the 85-ft telescope of the Harvard College Observatory in Fort Davis, Texas. Because of its location, this telescope was an important element in the US VLBI network until the VLBA began operation in 1994 with a new antenna at Fort Davis.
Ed supervised ten PhD students: Eugene Epstein (1962, HI in galaxies), Duane Muhleman (1964, Venus radar astronomy), G. Richard Huguenin (1964, long wavelength radio astronomy), Ellen Gundermann (1965, Galactic OH), Pat Palmer (1967, radio recombination lines), Ben Zuckerman (1968, OH masers), John Ball (1969, OH masers), Eric Chaisson (1972, radio recombination lines), Charles Lada (1975, molecular clouds), and Brian Connor (1985, atmospheric spectroscopy).
Ed was awarded the first Bart J. Bok Prize in 1958, an early-career award given annually to outstanding graduate of the Harvard Astronomy Department. He was an Alfred P. Sloan Fellow (1958-1964) and a member of the American Academy of Arts and Sciences.
Ed retired in 1996. Shortly after his retirement he moved to Fort Davis, Texas, and subsequently to Bradford, Vermont, and Chevy Chase, Maryland. He had many hobbies, the foremost of which was photography. He earned spending money as a commercial wedding photographer while in high school and college. His early photographs of historic buildings in Mobile were published in a book, Remembering Mobile, by Caldwell Delaney in 1948. While living in Fort Davis he undertook a photographic study of the phenomenon known as the Marfa lights (aka ghost lights of Texas). Although they have often been reported as UFOs, they are probably some sort of atmospheric refraction phenomenon involving automobile headlights or other lights on the ground. He specialized in black-and-white photography and won many awards in juried shows during his retirement.
Ed lived to be 92 even though he had had a heart attack in 1965 at age 37. He was mentally sharp to the end of his life but increasingly debilitated from Parkinson’s disease. He died unexpectedly and peacefully while sitting in his favorite chair on the evening of August 1, 2020.
1 Students in Bart Bok’s program in 21 cm HI radio astronomy included A. Edward Lilley (1955), David S. Heeschen (1955), Thomas Matthews (1956), T.K. Menon (1956), Campbell Wade (1958), May Kassim (1958), Nan Dieter (1958), William Howard (1958), and Frank Drake (1959). Bok left Harvard 1956, and students after that time were co-supervised by other department members.