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Farrokh Vakili coauthored a modern stellar intensity interferometry experiment using two one-metre optical telescopes separated by fifteen metres. The team correlated photon-counting signals from bright stars, reviving a technique historically associated with Robert Hanbury Brown.

The measured quantity was the zero-delay correlation between detected light intensities. Its contrast contains information about angular source structure. The team measured reliable visibilities for two marginally resolved stars and found reduced contrast for a binary star, consistent with its more extended apparent structure.^[ref]

Robert Hanbury Brown and Richard Q. Twiss sought angular sizes through correlations of detected light intensities. Their method multiplies detector outputs after detection, whereas a Michelson interferometer combines fields before detection.^[ref]

A monochromatic discharge source illuminated a half-silvered beam splitter and two photodetectors. The averaged current product showed an excess near coincidence. Moving one detector introduced a delay that removed it, supplying a control. Slow response weakened the peak. This photon bunching is compatible with fluctuating classical light intensity.^[ref]

A physicist who, with Robert Hanbury Brown, developed optical stellar intensity interferometry. Correlations between detected intensity fluctuations reveal spatial coherence even when the optical phases at the detectors are not directly combined. Their experiment on Sirius connected this correlation measurement to stellar angular size, providing an astronomical application of the Hanbury Brown and Twiss effect.^[ref]

Robert Hanbury Brown and Richard Quentin Twiss developed intensity interferometry, using correlated fluctuations in detected light rather than direct combination of optical field amplitudes. Their experiments established how the correlation changes with the separation between detectors.

Applied to stars, the method connects spatial coherence to apparent angular size. It measures a statistical property of the arriving photons, allowing stellar diameters to be inferred even when atmospheric fluctuations make direct optical phase measurements difficult.^[ref][ref]

In their 1956 Sirius report, Robert Hanbury Brown and Richard Q. Twiss used two 1.56-m searchlight reflectors feeding photomultipliers. The photocurrent fluctuations passed through 5–45-MHz amplifiers; an adjustable delay aligned arrival times. A linear mixer multiplied the outputs; an integrating motor accumulated their product. A second motor monitored its root-mean-square fluctuation to control gain changes. Separate lamps illuminated capped photomultipliers before and after observations to test electronic coupling and drift; blank-sky runs tested correlated sky background. They fitted a uniformly bright disk and an unknown zero-baseline scale to relative correlations at different interferometric baselines. Broadband response and possible baseline-dependent systematic errors limited the diameter inference.^[ref]

This astronomical test extends the preceding laboratory Hanbury Brown and Twiss effect to two independently collected samples of a star. The historical motor reading was an instrument-specific correlation statistic. It should not be identified numerically with the normalized $g^{(2)}$ below without the corresponding measurement calibration.