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Standard Candle techniques can only be used to determine the exact distance from Earth to another standard candle, right?

I mean, imagine I want to know the distance to a star A in galaxy $\alpha$. In galaxy $\alpha$, close to the star A, I notice there is a Type I Cepheid and I measure its apparent magnitude (m), I calculate the absolute magnitude (M) - using the Luminosity ($L$) I know -, and finally I get $d_L$.

So now I claim that the distance from Earth to Galaxy $\alpha$ is $d_L$?? And I can also claim that, within some error, the distance from Earth to star A is also $d_L$. Is this what astronomers do?

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Yes, that's how it's done. You can see that it furnishes an estimate rather than a precise answer; that estimate can be improved by other techniques that astrophysicists have in their toolbox.

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