Cosmic distance ladder
= Cosmic distance ladder
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Geometrical distances to nearby calibrators determine the luminosities of indicators that can be observed farther away. Those indicators calibrate still more luminous indicators in turn. A ladder may connect parallax or maser distances to <Cepheid variables> and then to <Type Ia supernovae>. Each step propagates its calibration uncertainty to the final distance scale and the inferred <Hubble constant>.