Aperture synthesis reconstructs the sky's brightness from complex visibilities measured at different interferometric baselines. Each measurement constrains a Fourier transform component of the brightness, rather than supplying a little photograph. Combining many such components can distinguish sources that each individual antenna leaves unresolved. The remarkable economy is that changing separations and the rotation of Earth can provide many measurements with only a few physical antennas.
Martin Ryle's Cambridge group made aperture synthesis a practical method of astronomical imaging at the Mullard Radio Astronomy Observatory. Cambridge's institutional history connects that work with the One-Mile Telescope and its larger successors.[ref]
Mullard Radio Astronomy Observatory at Lord’s Bridge by Cavendish Laboratory, University of Cambridge. Cavendish Laboratory, Mullard Radio Astronomy Observatory at Lord’s Bridge, sections Foundation and early development and A centre for radio interferometry
In his 1974 lecture Radio Telescopes of Large Resolving Power, Martin Ryle recalled the problem of distinguishing weak extragalactic sources and resolving their structure. He explained sequential wavefront sampling using one simultaneously observed element as a wave phase reference, and the saving obtained by letting Earth rotate the apparent baseline.[ref]
Radio Telescopes of Large Resolving Power by Martin Ryle. Ryle (1974), Radio Telescopes of Large Resolving Power, pp. 187–192, Figures 1 and 4
The 1974 Nobel Prize in Physics distinguished Martin Ryle's observations and inventions, especially aperture synthesis, from Antony Hewish's role in discovering pulsars. The latter is a separate astronomical discovery, with its own observational history.[ref]
The Nobel Prize in Physics 1974 by Nobel Prize Outreach. Nobel Prize in Physics 1974, award explanation and equal prize shares
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