BVRI photometry of extragalactic cepheids and new insights for the distance scale

The authors present new BVRI photoelectric photometry of long-period Cepheids in the Large and Small Magellanic Clouds. Period-luminosity relations based on both time-averaged and single, random-phased data are discussed, and it is shown that at wavelengths longward of the R bandpass the randomly phased data should give a spread at fixed period which is always less than the time-averaged B period-luminosity relation. Single-epoch data for five Cepheids measured in CCD exposures of a single field in M33 are used to illustrate the power of the random-phase period-luminosity relation for the Cepheid distance scale.