ON THE CHANGES OF PERIODS OF RR LYRAE VARIABLES IN THE GLOBULAR CLUSTERS M5, M53 AND NGC 5053

The period of a variable star is very sensitive to extremely minor changes in luminosity, mass, radius, surface temperature, etc. of the star. With new theoretical calculations of the interior structure of stars in the late stages of evolution now available, the investigation of instabilities in the periods of the RR Lyrae variables in globular clusters becomes urgent.