Transcript: Just like a bell or any mechanical object, stars have a particular frequency or timescale when they tend to vibrate in response to an external disturbance. If the time that it takes for energy to dam up in the atmosphere of a giant star corresponds to the natural frequency the star will oscillate or pulsate. These are regular variables. In stars where the timescale of the damming of radiation in the atmosphere and the oscillation timescale are not synchronized the variations are irregular. The complex behaviors of variable stars have led to a zoo of categories of variable stars.