What term describes a Cepheid variable used because its true luminosity (absolute magnitude) is known?
Answer
Standard candle
A Cepheid variable functions as a standard candle, which is a physical object whose true intrinsic brightness, or absolute magnitude, is known once its measurable characteristic—in this case, the period of pulsation—is determined. Astronomers use this known absolute magnitude and compare it directly to the magnitude they observe from Earth (apparent magnitude). The difference between these two values provides the necessary information, based on the principles of light fall-off over distance, to calculate how far away the standard candle is situated in space.
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