What additional information must astronomers determine to convert an exoplanet's relative size from transit data into an absolute physical size?

Answer

The actual physical size of the host star

Since transit photometry yields a relative size (planet radius to star radius), astronomers must independently determine the host star's actual physical size, often estimated via its spectral type, temperature, and luminosity, to calculate the planet's absolute radius.

What additional information must astronomers determine to convert an exoplanet's relative size from transit data into an absolute physical size?

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