How separate radio antennas work together to reveal smaller details
Interferometry combines signals across distances, with both widely spaced and compact arrays contributing to an astronomical image.
Explainer
Explainer: A radio telescope does not always need one enormous dish to distinguish fine detail in the sky. An array can combine signals from separate antennas using a technique called interferometry.
The distance between a pair of antennas is its baseline. For a given observing wavelength, longer baselines allow finer angular detail to be measured. This is why an array spread across kilometers can resolve features that a single dish of similar size could not distinguish.
The signals are combined through precise measurement and computation. Different antenna pairs sample different aspects of the sky’s brightness, and Earth’s rotation changes their orientation relative to the target. Together, those measurements provide information from which an image can be reconstructed.
Longer separation is not automatically better for every question. Widely spaced antennas can miss broad, diffuse structures. Compact configurations and additional single-dish measurements help recover larger-scale information, complementing the fine detail measured by long baselines.
ALMA uses this approach in Chile, with antennas that can be arranged at different separations and a compact array that adds information on extended sources. Its behavior is therefore different from a solid dish physically filling the whole area between antennas. The method’s strength comes from matching the measurements to the object: resolving a small structure while retaining enough information about its wider setting to interpret it correctly.
