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How does absolute magnitude allow astronomers to compare stellar brightness?

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Open cluster NGC 290 — Star Stars in the open cluster NGC 290, as seen by the Hubble Space Telescope.

Astronomers use absolute magnitude to compare the intrinsic luminosity of stars by removing the variable of distance from the equation.12

While apparent magnitude measures how bright a star appears from Earth—which is heavily influenced by how far away the star is—absolute magnitude standardizes this measurement. It is defined as the brightness a star would exhibit if it were viewed from a standard distance of 10 parsecs (32.6 light-years).234

By placing all stars at this theoretical, uniform distance, astronomers can directly compare their true energy outputs. This allows for the classification of stars based on their actual physical properties, such as distinguishing between giant and dwarf stars, rather than simply noting how bright they happen to look from our perspective on Earth.125