What is a variable star?

The night sky seems to be constant and unchanging (except for the movements of the Moon and planets). It was this view of the heavens as perfect that made life difficult for early astronomers such as Galileo . However, a large number of stars are actually variable stars that change in brightness either periodically or irregularly. The change can have many different causes. The most famous variable star - Algol - consists of two stars revolving around each other. When one moves in front of the other, the system appears dimmer from Earth.

One particular type of variable star has proved invaluable for helping to determine stellar distances. This is a type known as a Cepheid Variable.

* Click here to find out more about Cepheid Variables (Cepheids)

* Click here to learn how Cepheids can help us calculate distances

* Click here to find out how the brightness of a star is measured