Exoplanet transit methods
Transit time variation is a method for detecting exoplanets in other constellations and for observing variations in the time of a transit. This provides a sensitive method capable of detecting additional planets in systems beyond of ours with masses potentially as small as Earth's. In very compact planetary systems, the gravitational attraction of the planets between them causes one planet to accelerate and another planet to decelerate along its orbit. Acceleration causes the orbital period of each planet to change. Detection of this effect by measuring change is known as traffic time variations.
Radial velocity Doppler spectroscopy method of exoplanets
Doppler's spectroscopy, also known as radial velocity measurement, is a spectroscopic method for finding extrasolar planets. It involves the observation of Doppler displacements in the spectrum of the star around which the star orbits. A series of observations are made of the spectrum of light emitted by a star. Periodic variations in this spectrum can be detected, with the characteristic wavelength of spectral lines in the spectrum increasing and decreasing regularly over a period. These variations may be indicators that the radial velocity of the star is sent sinking by the presence of planets orbiting it, causing Doppler landslides in the star.