Doppler spectroscopy (or radial velocity) method uses radial velocity measurements from the Doppler shifts of the light from the parent star of the planet. This method utilizes the fact that a parent star experiences a slight gravitational pull from the planet orbiting it, as a result the star does not remain stationary but rather moves in a circular motion. In this way when the star moves towards the Earth, the light spectrum is blue shifted and when moving away from the earth it becomes red shifted. Doppler spectroscopy allows the minimum mass to be found of the planet2.
When a planet passes in front of its parent star, from the observer’s point of view the light given out by the star dims slightly. This is the Transit method of detecting exoplanets2.
Direct imaging can be used to find exoplanets by taking pictures of the bright star and correspondingly using a coronograph to block out the stars light enabling the planet to become visible2.