Variable Stars

I already had this on my page, but here's the link to make it more easily accessible. Yes, I know it's Wikipedia, but the information is pretty legitimate. And it is a bit long, but even a scan through can get some good points. --Joey Romero 18:52, 24 July 2010 (PDT)
Variable Stars on Wikipedia
The main points I got out of this are:

1. Variable stars are classified as either intrinsic or extrinsic. Intrinsic is when the star itself is pulsating or having some sort of eruptions, causing the change in brightness. Extrinsic is when the star's brightness is blocked by another orbiting star.
2. Specifically, I think the ones we've been studying are considered cepheids, or variable stars with shorter periods like days or months and their variation isn't very varying (say that five times fast! The site calls their luminosities "regular.")
3. Helium is the main cause of cepheids' fluctuations. Ionization, to be exact; gotta love chemistry.