| Pulsating variables are usually giant or supergiant stars that actually changes it diameter with time - periodically expanding and contracting, varying in temperature and magnitude. Their expansion and contraction can be measured by using the Doppler effect. The spectral lines shift toward the blue as the surface of the star moves toward us, and then to the red as it shrinks back. As the star pulsates, it changes overall color, indicating that its temperature is also varying. Most important, the luminosity of the pulsating variable also changes in a regular way. The four most common types are Cepheid, RR Lyrae, long-period, and irregular variables. |