Final answer:
Variable stars are stars that vary in brightness and are important for measuring distances in astronomy. Pulsating variable stars, such as cepheids and RR Lyrae variables, change their diameter, color, and luminosity as they expand and contract.
Step-by-step explanation:
Variable stars are stars that vary in brightness. They are important for measuring distances to remote parts of the galaxy and other galaxies. There are two types of special variable stars, cepheids and RR Lyrae variables, which are pulsating variable stars. Pulsating variables change their diameter and overall color as they expand and contract. The luminosity of the pulsating variable also changes in a regular way.