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closure phaseThe sum of phases around a loop of baselines in an interferometer containing three or more elements. When applied to a radio interferometer, the sum is unaffected by phase drifts in the receivers or by variations in the ionosphere or troposphere above the telescopes and is therefore determined solely by the radio source under observation. The basic idea is used extensively in VLBI and in optical aperture-synthesis telescopes.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006