Astronomer Jerry Nelson, inventor of the segmented mirror primary telescope mirror, and innovator in the field of adaptive optics, passed away in his sleep on June 9 at age 73.

Jerry Nelson graduated with a degree in physics from Caltech and a Ph.D. in particle physics from the University of California, Berkeley. He developed the concept of the segmented mirror telescope in the late 1970s. For decades the largest optical telescope in the world was the 5-m Hale telescope on Mt. Palomar, constructed in the 1940s. Building yet larger telescopes was considered impractical  because the conventional giant mirrors would be so heavy they would sag and distort under their own weight. Jerry (with a physicist’s perspective on the rapidly evolving capabilities of computers and electronics) realized that rather than one monolithic mirror, an array of small segments could also focus starlight, provided that a computer-controlled  servo mechanism could keep them precisely aligned. He also developed innovative techniques to mass-produce such segments.

These ideas made possible the design and construction of the W.M. Keck telescope I, which went into operation in 1993, together with its twin.  These 10m-segmented primary mirrors have revolutionized astronomy, with discoveries the include determining the mass of the black hole in the center of our galaxy to the first images of a system of extrasolar planets . Jerry’s segmented-mirror concept opened the possibility of building, for a relatively low cost, telescopes of very large sizes. This concept will also been taken into space because NASA’s James Webb Space Telescope, which will be launched in 2018, has a 6.5 m-segmented aperture, almost three times larger than the Hubble Space Telescope.  Jerry Nelson is without doubt the father of the W.M. Keck telescopes and the pioneer who allowed astronomers to conceive of and design a future generation of large segmented telescopes now under construction, including the Thirty Meter Telescope and the European-Extremely Large Telescope.

In 2000, Nelson founded the Center for Adaptive Optics (CfAO), a National Science Foundation Science and Technology Center based at UC Santa Cruz. The center’s goal was to pioneer the use of adaptive optics (AO) in astronomy, taking full advantage of the large apertures offered by ground-based telescopes.

“I met Jerry Nelson shortly after I arrived in the United States in November 2000. I remember how he welcomed us with his smile, his large collection of Hawaiian shirts, and stories on the design of the Keck telescopes,” notes Senior Planetary Astronomer Franck Marchis of the SETI Institute, a member of the CfAO until 2010. “He often reminded us of how important the development of adaptive optics was for these large telescopes, and always had kind words when we presented our observations of Io, asteroids, and other solar system bodies taken with the W.M. Keck AO system.”

The CfAO has been a successful incubator of ambitious adaptive optics projects in the fields of astronomy and biological imaging. Nelson has touched and transformed the lives of an enormous number of astronomers with his work in adaptive optics.

“Jerry was one of the most brilliant people I knew but also one of the nicest —always engaged intellectually with anyone who wanted to talk in an open and friendly way. I learned a huge amount about telescopes and instruments from many lunches at the CfAO. I miss talking to him, his humor and intelligence and friendliness,” remembers Prof. Bruce Macintosh of Stanford University, Principal Investigator of the Gemini Planet Imager, an AO-based instrument designed to search for Jupiter-like exoplanets.

According to the University of California Santa Cruz News Center, a symposium to honor Nelson is planned for July 13 and 14, 2017, in Santa Cruz. The gathering, which is set to feature talks by many eminent astronomers who worked with him over the years, will now serve as a memorial and a celebration of his life.

“Jerry held up the beacon of excellence, showing us that together we could achieve more than we ever dreamed,” said W.M. Keck Observatory Director Hilton Lewis. “We have lost Jerry, but his inspiration and humanity will live on”.