rr lyrae stars and their distances

rr lyrae variables play an important role in several fields of stellar evolution and cosmology, moreover, they are the most popular primary standard candles for population ii stellar systems. in this paper, their properties are examined within the framework of modern computations of stellar evolution and pulsation models in order to discuss their use as distance indicators. the comparison between selected observed data and predicted relations, for the determination of both apparent and intrinsic distance moduli, is also presented.