Astrometry Method to Detect Exoplanets

Astrometry is the science of precisely measuring the position of the objects in the sky. The gravity of a planet, however weak it might be, is enough to pull it’s parent star just a little bit out of place as the planet orbits. While the radial velocity method studies a star’s spectrum to measure the star’s ’wobble’ toward and away from earth, there is a another trick to measure this tell-tale motion: simply look for the star to move back and forth in the sky. With exceptionally sharp vision, a telescope can actually see a star move relative to other stars. If astronomers use this method to monitor a star and see that it sways away with a periodic rhythm, then they can tell that an unseen companion - perhaps a planet - is orbiting the star and pulling it to and fro.