Multicolor photometric observations of a planetary transit in the system HD 209458 are analyzed. The observations, made in the Strömgren photometric system, allowed a recalculation of the basic physical properties of the star-planet system. This includes derivation of linear limb-darkening values of HD 209458, which is the first time that a limb-darkening sequence has observationally been determined for a single late main-sequence star beyond the Sun. As the derived physical properties depend on assumptions that are currently known with limited precision only, scaling relations between derived parameters and assumptions are given. The observed limb-darkening is in good agreement with theoretical predictions from evolutionary stellar models combined with ATLAS model atmospheres, verifying these models for the temperature (Teff~6000 K), surface gravity (/log g~4.3) and mass (~1.2 Msolar) of HD 209458.