= Observational astronomy
{wiki}
<Observational astronomy> infers astronomical properties from measured <light>, particle arrivals, positions and time variations. A detector first measures counts or signals; <calibration>, the <point spread function>, background and selection effects connect those data to an <observed radiative flux> or an inferred source parameter.
Different observables constrain different quantities. <Spectroscopy> supplies line shifts and composition-sensitive features, <astrometry> supplies positions and apparent motions, and a <light curve> supplies temporal structure. Their combination can break ambiguities that remain in a single observation. An <astronomical selection function> is then needed to infer a population from the objects that were detected.
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