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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]

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]

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]

Jocelyn Bell Burnell helped build Antony Hewish's radio telescope for finding compact sources through interplanetary scintillation in the solar wind. Operating it and inspecting its chart recorder output in 1967, she recognized an unusual recurring trace, checked earlier charts, and obtained fast recordings resolving pulses in late November. Her observation, recognition and persistent analysis were indispensable.^[ref]

The 1968 paper by Antony Hewish, Jocelyn Bell Burnell (bylined S. J. Bell), J. D. H. Pilkington, P. F. Scott and R. A. Collins reported $1.337\mathrm{s}$ spacing and proposed compact-star oscillations. Its radio telescope had 2,048 full-wave dipole antennas in sixteen rows. Four receivers selected declinations; two array halves formed an east-west interferometer. The $81.5\mathrm{MHz}$ receivers passed $1\mathrm{MHz}$. Observations used $0.05\mathrm{s}$ receiver time constant and Rapidigraph chart recorder with $0.03\mathrm{s}$ time constant; radio second pips calibrated timing.^[ref]

Antony Hewish checked sidereal time recurrence. Jocelyn Bell Burnell recalls that P. F. Scott and R. A. Collins reproduced the pulses with another telescope and receivers, while J. D. H. Pilkington measured pulsar dispersion delay: independent checks of instrument independence and intervening plasma.^[ref]

A useful numerical comparison uses the approximate sidereal time day of $1436.07\min$. Relative to a $1440\min$ schedule, the same sky direction transits about $3.93\min$ earlier each day, or $39.3\min$ after ten days. This compares successive passages through the receiving beam; it is a different clock from the roughly $1.3\mathrm{s}$ pulse spacing within one passage. Sky recurrence alone cannot rule out every transmitter or reflection, and pulsar dispersion delay alone does not uniquely establish an emission mechanism. Their strength lies in independent constraints agreeing.

The discovery lesson is that an unexpected signal must survive changes of readout, instrument and observing date. Increasing chart recorder speed exposed structure hidden in a compressed trace; it did not make the source begin pulsing. The pulsar interpretation now separates the rotating clock, beam geometry, pulsar magnetosphere emission and pulsar dispersion delay. The initial observation established periodic arrival, not a direct measurement of the neutron star's surface motion or radius.

Awarded in equal shares to Martin Ryle and Antony Hewish for pioneering radio astrophysics: Ryle for observations and inventions, especially aperture synthesis, and Hewish for his decisive role in discovering pulsars.^[ref]