eli5: How does brightness determine distance if stars come in different sizes and colors?

Question

eli5: How does brightness determine distance if stars come in different sizes and colors?

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Answer 1

Stars do come in different sizes and colors, but they don’t come in *infinite* sizes and colors. [There are classes of stars](https://en.wikipedia.org/wiki/Stellar_classification) and their brightness and “colors” they emit (as a result of their composition and the types of nuclear reaction that they’re undergoing) are more or less understood. You can see that the wikipedia article includes “luminosity” for each class of stars.

So it’s more like “Ok based on the spectral colors, that’s an O-class giant, it should be this bright but we’re only seeing it as this bright, therefore [quick math] it’s this far away.”