Radial Velocity Method to Detect Exoplanets

Radial Velocity method uses Gravity to detect planets. A planet is much smaller than it's star, but it still exerts a tiny gravitational pull or tug, on the star as it orbits. When a planet is behind the star (from our point of view), it pulls the star slightly away from us. When it's in front, it pulls the star slightly toward us. This causes the star to wobble back and forth. Astronomers look for this wobbling to find planets. Now how do astronomers detect this wobble? Well, they use something called a spectrograph and powerful telescopes to examine the light coming from a star. A spectrograph, like a prism, splits the light from the star into its component colors producing a spectrum. Some of the starlight gets absorbed as it passes through the star's atmosphere, and this produces small, dark gaps or lines in the spectrum. As the star moves closer to us, these lines shift toward the blue end of the spectrum. As the star moves away, the lines shift back toward the red e