Cepheid Variable Stars
Cepheid variable stars are often used as distance calibrators for nearby
galaxies. They are very luminous yellow giant or supergiant stars,
regularly varying in brightness with periods ranging from 1 to 70 days.
This type of star is in a late evolutionary stage, pulsating due to an
imbalance between its inward gravitational pull and outward pressure.
Cepheids are found in remote open clusters whose distances are known
from comparison with nearby open clusters. It is, therefore, possible to
calibrate these Cepheids with an independently obtained ruler ot yardstick.
For nice animations for how Cepheid variables pulsate,
go to the Space
Telescope Science Insitute webpage on
M100 press release.