What must astronomers determine with high accuracy to calculate true luminosity from apparent brightness?

Answer

The distance from Earth

Because apparent brightness ($b$) is mathematically related to luminosity ($L$) and distance squared ($d^2$) by the formula $b = L / (4 gtr d^2)$, any error in distance measurement propagates into a massive error when calculating the intrinsic energy output ($L$).

What must astronomers determine with high accuracy to calculate true luminosity from apparent brightness?

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Astronomy - Measuring Distance, Size, and Luminosity (1 of 30 ...

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