There are many types of variable stars, and their brightness changes due to various reasons:
* Cepheid variables: These stars pulsate, expanding and contracting, causing their brightness to change in a predictable pattern. They are incredibly important for astronomers as they have a direct relationship between their pulsation period and their absolute brightness. This allows us to determine their distance from Earth.
* Eclipsing binaries: These are systems of two stars orbiting each other, where one or both stars eclipse each other from our point of view. The apparent brightness of the system changes as the stars block each other's light.
* RR Lyrae variables: These stars also pulsate, similar to Cepheid variables, but are less luminous and have shorter periods. They are found in globular clusters and are used to determine distances to these clusters.
So, the next time you see a star that seems to flicker or change its brightness, you might be witnessing a variable star at work!
