Multicolor observations of a planetary transit of HD 209458

We present BVRIZ photometric observations of HD 209458 during the transit b y its planetary companion on UT 1999 November 15 with the University of Haw aii 0.6 and 2.2 m telescopes and the High Altitude Observatory STARE telesc ope. The detailed shape of the transit curve is predicted to vary with colo r primarily as a result of the color-dependent limb darkening of the star b ut potentially due as well to the effect of color-dependent opacity in the planetary atmosphere. We model the light curves and present refined values for the transit timing and orbital period, useful for planning future obser vations of the planetary transit. We also derive significantly improved mea surements of the planetary radius, R-p = 1.55 +/- 0.10 R-Jup, stellar radiu s, R-s = 1.27 +/- 0.05 R., and orbital inclination, i = 85.degrees 9 +/- 0. degrees 5. The derived planetary radius favors evolutionary models in which the planet has a low albedo.