Radio interferometry

Radio interferometry combines signals from separated radio telescopes to synthesize an aperture larger than any single dish, achieving fine angular resolution.

Interferometer: An instrument that combines waves from multiple paths to measure properties such as phase, frequency, or intensity. Radio arrays are a specialized form of interferometer that correlates signals from separate antennas.
Very Long Baseline Interferometry: Radio interferometry using antennas separated by intercontinental or larger distances, often recorded independently and correlated later. It pushes radio angular resolution to the scale set by Earth-sized baselines.
Radio astronomy: The study of celestial objects and phenomena through their radio-frequency emission. Radio interferometry is a principal method for obtaining detailed images in this field.
Single-dish radio telescope: A radio telescope that collects radiation with one dish rather than combining signals from separated antennas. A single dish offers simpler measurements, while an array can attain finer resolution with long baselines.
Square Kilometre Array: An international radio astronomy observatory being built in Australia and South Africa, designed for unprecedented survey sensitivity. Its scale will test how arrays manage immense data rates while surveying the radio sky.
Baseline (interferometry): The separation vector between two antennas or telescopes in an interferometric array. Baseline length and orientation set the angular scales sampled by the array.
Event Horizon Telescope: A global network of radio observatories that operates as an Earth-sized interferometer. Its 2019 image of M87* demonstrated interferometric imaging of a black hole's shadow.
Electromagnetic radiation: Energy carried through space by oscillating electric and magnetic fields. The array combines the phases and amplitudes of this radiation at radio wavelengths.
Optical interferometry: The combination of visible or infrared light from separate telescopes to measure angular structure. It shares the interference principle but faces different detector, atmosphere, and signal-combination constraints.
Radio-frequency interference: Unwanted radio emissions from human or natural sources that contaminate astronomical observations. Increasing communications and electronics make interference mitigation essential for sensitive arrays.

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