What physical law connects the measured apparent brightness of a standard candle to its true luminosity?

Answer

The inverse-square law of light

When the actual light output (luminosity) of an object is known, the inverse-square law of light can be used, relating that true output to how dim it appears from the observer's position, thereby yielding the distance.

What physical law connects the measured apparent brightness of a standard candle to its true luminosity?

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