Kenneth Irwin Kellermann

Kenneth Irwin Kellermann


Date of Birth
July 1, 1937

“Ken” Kellermann was born in New York and earned his S.B. in physics at the Massachusetts Institute of Technology in 1959 and his Ph.D. in physics and astronomy at the California Institute of Technology in 1963. He switched from physics to radio astronomy after John Bolton conscripted him as a graduate student assistant. The Owens Valley Radio Observatory was still being built, and Kellermann was one of the first to use its two-element interferometer, completing his Ph.D. under Gordon Stanley with measurements of spectra of both galactic and extragalactic radio sources. He spent part of his graduate studies visiting Martin Ryle’s group at the University of Cambridge. After postdoctoral research with Bolton at the CSIRO Division of Radiophysics, where he observed thermal emission from planets with the relatively new Parkes telescope, he joined the National Radio Astronomy Observatory in 1965. He has been at NRAO ever since, with a few leaves at Leiden, Sydney, Caltech, and Germany, where in 1978 and 1979 he was a Director at the Max Planck Institute for Radio Astronomy, and he has held a concurrent appointment as research professor of astronomy at the University of Virginia. He has served as NRAO’s Acting Assistant Director for Green Bank Operations, as Chief Scientist, and as head of its New Initiatives Office.

Starting in the late 1960s, Kellermann, Barry Clark, and Marshall Cohen became some of the early leaders in the development of Very Long Baseline Interferometry. Soon they were achieving one milliarcsecond resolution, far surpassing optical telescopes, and making maps of galactic and extragalactic radio sources, using antennas in Green Bank together with others in California, Massachusetts, Puerto Rico, and then Sweden, Australia, Germany, and Russia. It was difficult to arrange time and collaboration with many different telescopes, each with its own schedule of observations, so in 1974 a group was organized to design a dedicated array of identical telescopes spread over a large distance. Kellermann led the effort, which took nearly two decades and resulted in the 1993 dedication of the Very Long Baseline Array, with ten 25-m telescopes spread from Hawaii to the U.S. Virgin Islands. He has also been a strong advocate for using radio telescopes in space along with terrestrial ones to achieve even greater baselines and thus higher angular resolution. This has been achieved with Japanese and Russian satellites, the latter leading to observations of active galactic nuclei with unprecedented angular resolution. He was involved from the start in the international project to develop the Square Kilometre Array.

Kellermann’s research, conducted in collaboration with many colleagues, has included gradually increasing the limits of sensitivity of radio telescopes to sources six orders of magnitude weaker than when he started in the field, and making detailed studies of extremely weak sources, often with very high resolution. He shared in the discovery of apparent superluminal motion, and he published the first paper in a refereed journal reporting on a radio search for extraterrestrial intelligence. He has been very active in national and international science policy, serving on a number of committees and panels. He has also contributed to the history of radio astronomy, editing books, writing articles, and promoting the development of the National Radio Astronomy Observatory Archives. He led in the successful efforts to obtain the papers of Grote Reber and other pioneers for these archives.

Personal web page

At the National Radio Astronomy Observatory.

Other awards

American Astronomical Society, Helen B. Warner Prize, 1971.
American Academy of Arts and Sciences, Rumford Prize, 1971 [shared].
National Academy of Sciences, Benjamin Apthorp Gould Prize, 1973.

Biographical materials

Dunn, Peter, MIT Technology Review, 2014.
NRAO, with finding aid to his papers

Academic genealogy



National Radio Astronomy Observatory (several)
American Institute of Physics (two)

Named after him

Minor Planet #152985 Kenkellermann


Papers, etc.

Kellermann’s papers from 1965 to 2011 are at the National Radio Astronomy Observatory Archives. The archives also contain an oral history interview conducted by W.T. Sullivan, III in 1975.

Other References: Historical

Kellermann, K.I. & M.H. Cohen, “The Origin and Evolution of the N.R.A.O.-Cornell VLBI System,” JRASC 82, 248-65 (1988).

Kellermann, Ken I., Wayne Orchiston, & Bruce Slee, “Gordon James Stanley and the Early Development of Radio Astronomy in Australia and the USA,” Publications of the Astronomical Society of Australia 22, 13-23 (2005).

Kellermann, K.I., “Early Parkes Observations of Planets and Cosmic Radio Sources,” in R. Braun, ed., Proceedings of the Conference “Science with Parkes @ 50 Years Young,” held at Parkes, Australia, 31 October to 4 November 2011 [pdf].

Kellermann, K.I., “The First U.S.-U.S.S.R. VLBI Observations,” in F.J. Lockman, F.D. Ghigo, & D.S. Balser, eds., But It Was Fun: The First Forty Years of Radio Astronomy at Green Bank (NRAO, 2007), pp. 541-62.

Kellermann, K.I., “Breaking the Milliarcsecond Resolution Barrier,” in Proceedings of Resolving the Sky - Radio Interferometry: Past, Present and Future, Manchester, UK, 17-20 April 2012PoS(RTS2012)003.

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Other References: Scientific

Kellermann, K.I., R.J. Long, L.R. Allen, & M. Moran, “A Correlation between the Spectra of Non-thermal Radio Sources and their Brightness Temperatures,” Nature 195, 692-93 (1962).

Conway, R.G., K.I. Kellermann, & R.J. Long, “The radio frequency spectra of discrete radio sources,” MNRAS 125, 261-84 (1963).

Kellermann, Kenneth I., The Spectra of Galactic and Extragalactic Radio Sources (Ph.D. Dissertation, California Institute of Technology, 1963).

Kellermann, K.I., “The Spectra of Non-Thermal Radio Sources,” Ap.J. 140, 969-91 (1964).

Pauliny-Toth, I.I.K. & K.I. Kellermann, “Variations in the Radio-Frequency Spectra of 3C 84, 3C 273, 3C 279, and Other Radio Sources,” Ap.J. 146, 634-45 (1966).

Kellermann, K.I., “On the Interpretation of Radio-Source Spectra and the Evolution of Radio Galaxies and Quasi-Stellar Sources," Ap.J. 146, 621-33 (1964).

Kellermann, K.I., “The Radio Source 1934-63,” Australian Journal of Physics 19, 195-207 (1966).

Kellermann, K.I. & I.I.K. Pauliny-Toth, “Variable Radio Sources,” Ann. Rev. Astron. Astrophys. 6, 417-48 (1968).

Cohen, M.H., D.L. Jauncey, K.I. Kellermann, & B.G. Clark, “Radio Interferometry at One-Thousandth Second of Arc,” Science 162, 88-94 (1968).

Kellermann, K.I. & I.I.K. Pauliny-Toth, “The Spectra of Opaque Radio Sources,” Ap.J. 155, L71-L78 (1969).

Kellermann, K.I., I.I.K. Pauliny-Toth, & P.J.S. Williams, “The Spectra of Radio Sources in the Revised 3C Catalogue,” Ap.J. 157, 1-34 (1969).

Kellermann, K.I., “Thermal Radio Emission From the Major Planets,” Radio Science 5, 487-93 (1970).

Broderick, J.J., et al., “Observations of Compact Radio Sources with a Radio Interferometer Having a Green Bank-Crimea Baseline,” Soviet Astronomy 14, 627-29 (1971).

Cohen, M.H., et al., “The Small-Scale Structure of Radio Galaxies and Quasi-Stellar Sources at 3.8 Centimeters,” Ap.J. 170, 207-17 (1971).

Pauliny-Toth, I.I.K., K.I. Kellermann, M.M. Davis, E.B. Fomalont, & D.B. Shaffer, “The NRAO 5-GHz Radio Source Survey. II. The 140-ft "Strong", "Intermediate", and "Deep" Source Surveys,” Astronomical Journal 77, 265-84 (1972).

Pauliny-Toth, I.I.K. & K.I. Kellermann, “The NRAO 5-GHz radio source survey. III. The 140-ft ‘Strong’ Source Survey,” Astronomical Journal 77, 797-809 (1972).

Clark, B.G., et al., “Observations of Compact Radio-Emitting Objects at 3.55 cm with Maximum Angular Resolution,” Soviet Astronomy 16, 576-78 (1973).

Swenson, G.W., Jr. & K.I. Kellermann, “An Intercontinental Array—A Next-Generation Radio Telescope,” Science 188, 1263-68 (1975).

Cohen, M.H., et al., “Observations with a VLB Array. I. Introduction and Procedures,” Ap.J. 201, 249-55 (1975).

Schaffer, D.B., et al., “Observations with a VLB Array. II. The Sources 4C 39.25, NRAO 150, VRO 42.22.01, 3C 345, and 3C 454.3,” Ap.J. 201, 256-62 (1975).

Cohen, M.H., et al., “Observations with a VLB Array. III - The sources 3C 120, 3C 273B, 2134+004, and 3C 84,” Ap.J. 201, 263-74 (1975).

Cohen, M.H., et al., “Radio Sources with Superluminal Velocities,” Nature 268, 405-09 (1977).

Yen, J.L., et al., “Real-time, Very-long-baseline Interferometry Based on the Use of a Communications Satellite,” Science 198, 289-91 (1977).

Pauliny-Toth, I.I.K., et al., “The 5 GHz Strong Source Surveys. IV. Survey of the Area between Declination 35 and 70 Degrees and Summary of Source Counts, Spectra and Optical Identifications,” Astronomical Journal 83, 451-74 (1989).

Schraml, J., I.I.K. Pauliny-Toth, A. Witzel, K.I. Kellermann, K.J. Johnston, & J.H. Spencer, “On the Superluminal Motion in the Quasar 3C 345,” Ap.J. 251, L57-L59 (1981).

Kellermann, K.I. & I.I.K. Pauliny-Toth, “Compact Radio Sources,” Ann. Rev. Astron. Astrophys. 19, 373-410 (1981).

Fomalont, E.B., K.I. Kellermann, & J.V. Wall, “Limits to the Small-scale Fluctuations in the Cosmic Background Radiation,” Ap.J. 277, L23-L26 (1984).

Kellermann, K.I. & A.R. Thompson, “The Very Long Baseline Array,” Science 229, 123-30 (1985).

Lo, K.Y., D.C. Backer, R.D. Eckers, K.I. Kellermann, M. Reid, & J.M. Moran, “On the Size of the Galactic Centre Compact Radio Source: Diameter < 20 au,” Nature 315, 124-26 (1985).

Kellermann, K.I. & G.A. Seielstad, eds., The Search for Extraterrestrial Intelligence: Proceedings of an NRAO workshop Held at the National Radio Astronomy Observatory, Green Bank, West Virginia, May 20, 21, 22, 1985 (NRAO, 1986) [[This book is available free as a 46-MB pdf at]

Kellermann, K.I., “Superluminal Radio Sources,” Comments on Astrophysics 11 (2), 69-81 (1985).

Kellermann, K.I. & Frazer N. Owen, “Radio Galaxies and Quasars,” in Verschuur, G.L. & K.I. Kellermann with E. Bouton, eds., Galactic and Extragalactic Radio Astronomy, 2nd ed. (Springer, Berlin & New York, 1988), pp. 563-602.

Kellermann, K.I.,R. Sramek, M. Schmidt, D.B. Shaffer & R. Green, “VLA observations of objects in the Palomar Bright Quasar Survey,” Astronomical Journal 98, 1195-1207 (1989).

Fomalont, E.B., R.A. Windhorst, J.A. Kristian, & K.I. Kellerman, “The Micro-jansky Radio Source Population at 5 GHz,” Astronomical Journal 102, 1258-77, 1575 (1991).

Kellermann, K.I., “The Cosmological Deceleration Parameter Estimated from the Angular-size/redshift Relation for Compact Radio Sources,” Nature 361, 134-361 (1993).

Kellermann, K.I., R.A. Sramek, M. Schmidt, R.F. Green, & D.B. Shaffer, “The Radio Structure of Radio Loud and Radio Quiet Quasars in the Palomar Bright Quasar Survey,” Astronomical Journal 108, 1163-77 (1994).

Cohen, Marshall H. & Kenneth I. Kellermann, “Quasars and Active Galactic Nuclei: High Resolution Radio Imaging,” Proc. Nat. Acad. Sci. 92, 11339-41 (1995).

Shaver, P.A., J.V. Wall, K.I. Kellermann, C.A. Jackson, & M.R.S. Hawkins, “Decrease in the space density of quasars at high redshift,” Nature 384, 439-41 (1996).

Fomalont, E.B., K.I. Kellermann, E.A. Richards, R.A. Windhorst, & R.B. Partridge, “Radio Emission from Objects in the Hubble Deep Field,” Ap.J. 475, L5-L7 (1997).

Kellermann, R.C. Vermeulen, J.A. Zensus, & M.H. Cohen, “Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei.,” Astronomical Journal 115, 1295-1318 (1998).

Richards, E.A., K.I. Kellermann, E.B. Fomalont, R.A. Windhorst,& R.B. Partridge, “Radio Emission from Galaxies in the Hubble Deep Field,” Astronomical Journal 116,1039-54 (1998).

Gurvits, L.I., K.I. Kellermann, & S. Frey, “The ‘Angular Size - Redshift’ Relation for Compact Radio Structures in Quasars and Radio Galaxies,” Astronomy and Astrophysics 342, 378-88 (1999).

Richards, E.A., et al., “Optically Faint Microjansky Radio Sources,” Ap.J. 526, L73-L76 (1999).

Kellermann, K.I. & J.M. Moran, “The Development Of High-Resolution Imaging In Radio Astronomy,” Ann. Rev. Astron. Astrophys. 39, 457-509 (2001).

Kellermann, K.I., et al., “Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. III. Kinematics of Parsec-scale Radio Jets,” Ap.J. 609, 539-63 (2004).

Wilkinson, P.N, K.I Kellermann, R.D Ekers, J.M Cordes, & T. Joseph W. Lazio, “The Exploration of the Unknown,” New Astronomy Reviews 48, 1551-1563 (2004).

Kovalev, Y.Y., et al., “Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine-Scale Structure,” Astronomical Journal 130, 2473-2505 (2005).

Lister, M L., et al., “MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. V. Multi-Epoch VLBA Images,” Astronomical Journal 137, 3718-29 (2009).

Lister, M L., et al., “MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. VI. Kinematics Analysis of a Complete Sample of Blazar Jets,” Astronomical Journal 138, 1874-92 (2009).

Kardashev, N.S., Y.Y. Kovalev, & K.I. Kellermann, “RadioAstron: An Earth-Space Radio Interferometer with a 350,000 km Baseline,” The Radio Science Bulletin 343, 22-29 (2012).

Condon, J.J.; K.I. Kellermann, Amy E. Kimball, Željko Ivezić & R.A. Perley, “Active Galactic Nucleus and Starburst Radio Emission from Optically Selected Quasi-stellar Objects,” Ap.J. 768, id 37 (2013).

Bonzini, M., et al., The sub-mJy radio sky in the Extended Chandra Deep Field-South: source population, MNRAS 436, 3759-71 (2013).

Vernstrom, T., et al., “Deep 3 Ghz Number Counts from a P(D) Fluctuation Analysis,” MNRAS 440, 2791-2809 (2014).

Homan, D.C., et al., “MOJAVE. XIX. Brightness Temperatures and Intrinsic Properties of Blazar Jets,” Ap.J. 923, id 67 (2021).

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Other Works: Popularizations, History, etc.

Kellermann, K.I., “Joint Soviet-American Radio Interferometry,” Sky & Telescope 42, 132 (1971).

Kellermann, K.I., “Intercontinental Radio Astronomy,” Scientific American 226, 72-83 (1972).

Kellermann, Kenneth I., “Extragalactic Radio Sources,” Physics Today 26 (10), 38-47 (1973).

Kellermann, K.I. & B. Sheets, eds., Serendipitous Discoveries in Radio Astronomy, Proceedings of a Workshop held at the National Radio Astronomy Observatory, Green Bank, West Virginia, May 4-6, 1983 (NRAO, Green Bank, 1984) [This book is available free as a 49-MB pdf at]

Kellermann, Kenneth I. & David S. Heeschen, “Radioastronomy in the 1990s,” Physics Today 44 (4), 40-45 (1991).

Kellermann, K.I., “Radio Astronomy: The Next Decade,” Sky & Telescope 82, 247-53 (1991).

Kellermann, Kenneth I., “Radio Astronomy in the 21st Century,” Sky & Telescope 93 (2), 26 (1997).

Kellermann, K.I., “Grote Reber’s Observations on Cosmic Static,” Ap.J. 525, 371-72 (1999).

Kellermann, K.I., “Grote Reber (1911-2002),” PASP 116, 703-11 (2004).

Kellermann, K.I., J.M. Cordes, R.D. Ekers, J. Lazio, & Peter Wilkinson, “The Exploration of the Unknown,” in Special Session 5: “Accelerating the Rate of Astronomical Discovery,” IAU meeting 11-14 August 2009, Rio de Janeiro, Brazil.

Braude, S.Y., et al., eds., A Brief History of Radio Astronomy in the USSR: A Collection of Scientific Essays (Springer, 2012) [Kellermann edited the English translation and was a coauthor of the preface.]

Kellermann, K.I., “The Discovery of Quasars,” Bulletin of the Astronomical Society of India 41, (1,1), 1-17 (2013).

Kellermann, K.I., “The Discovery of quasars and its aftermath,” Journal of Astronomical History and Heritage 17, 267-82 (2014).

Kellermann, Kenneth I., Ellen N. Bouton, & Sierra S. Brandt, Open Skies; The National Radio Astronomy Observatory and Its Impact on US Radio Astronomy (Springer, 2020.) [Digital version is free.]