Boksenberg, Alexander (1936– )

English astronomer and physicist who devised a light-detecting system that can be attached to telescopes, vastly improving their optical powers. His image photon-counting system (IPCS) revolutionized observational astronomy, enabling him and others to study distant quasars.

Boksenberg also designed instruments for ultraviolet astronomy, for use on high-altitude balloon-borne platforms and on satellites, particularly the observatory satellites TD-1 (1972) and the International Ultraviolet Explorer (IUE) (1978).

Boksenberg studied at London University, England. He became professor of physics there in 1978 and was director of the Royal Greenwich Observatory 1981–93. He was also director of the Royal Observatories 1993–96.

In the early 1960s Boksenberg became interested in the instrumentation carried aboard space vehicles, and in image-detecting systems. The IPCS, rather than recording light with a photographic emulsion, uses a television camera and a computer to detect and store the locations of individual photons of light collected by a telescope from a faint astronomical object, and to present the incoming results as an instantaneous picture. Successfully tested in 1973 at Mount Palomar, California, the invention was subsequently installed on all modern telescopes.

Boksenberg's study of the absorption lines in the spectra of quasars has shown that these are not a manifestation of the quasar itself but a reflection of the state of the universe – galaxies and intergalactic gas – that exists between the quasar and the Earth. They can thus provide direct information on the nature and evolution of the universe.