How do astronomers find planets outside our solar system?
During the past decade, astronomers have discovered far more planets outside our solar system — called extrasolar planets — than are located within it. Astronomers can not only detect a planet’s presence, they can deduce a lower limit to its mass and distance from its parent star, and the length of its year. The most successful search method used to date is called the “radial velocity” method. As a star is tugged to and fro by a planet’s gravitational pull, astronomers measure a slight shift in the frequency of the star’s light. “Astrometry” is another detection method. Its is sometimes called positional astronomy. Astronomers measure a star’s change in position on the sky, induced by the gravitational pull of a planet. They can use this information to calculate the planet’s mass and orbit. If a planet passes directly between a star and an observer’s line of sight, it blocks out a tiny portion of the star’s light. This so-called “transit method” is used to look for predictable variat
