Of the 130 extrasolar planets discovered to date, most have been found using the radial velocity method, where a planet causes tiny changes to a star's velocity compared to the Earth. This back and forth motion changes the wavelength of the light from our perspective. Another method, the transit method, has turned up 6 planets so far, and should find many more in the coming years. It works by watching for a star to dim slightly on a regular basis as a planet passes in between us and the star.