LIGO Document T1200427-v1

Methods of Measuring Astronomical Distances

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T - Technical notes
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The determination of source distances, from solar system to cosmological scales, holds great importance for the purposes of all areas of astrophysics. Over all distance scales, there is not one method of measuring distances that works consistently, and as a result, distance scales must be built up step-by-step, using different methods that each work over limited ranges of the full distance required. Broadly, astronomical distance `calibrators' can be categorised as primary, secondary or tertiary, with secondary calibrated themselves by primary, and tertiary by secondary, thus compounding any uncertainties in the distances measured with each rung ascended on the cosmological `distance ladder'. Typically, primary calibrators can only be used for nearby stars and stellar clusters, whereas secondary and tertiary calibrators are employed for sources within and beyond the Virgo cluster respectively. We discuss typical methods of distance determination on each step of the distance ladder, their distance reaches and the associated error of measurements gleaned using each method.
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