Three types of variable stars grow brighter and dimmer at regular intervals: Cepheids, RR Lyrae, and long-period variables (LPVs).
These stars are probably between old age and death.
Cepheids take anywhere from about 1 to 70 days to go from their brightest to their dimmest and back to their brightest.
The brightness of RR Lyrae varies during regular cycles that average less than 1 day.
LPVs’ brightness fluctuates at irregular intervals longer than 80 days.
The cycle for the LPV named Mira, for example, takes more than 300 days.
