One way of discovering exo-planets is by direct observations. You take a telescope point it in the right direction, this involves a lot of luck, and hope to spot a planet orbiting around a distant star.

This technique can be used to discover the moons of Jupiter, but because most of the stars are so far away, it quickly becomes impossible. Instead we should use our knowledge to infer the existence of exo-planets.

With direct observations out of the window, the alternative is indirect observation. This entails to take measurements of a star, analyze the data and infer the existence of exo-planets.

The following sections and chapters will provide some examples of this method.