Nevertheless, an extraterrestrial observer measuring the Sun's motion through space would detect a slight wobble in the Sun's path, a wobble with a period of twelve years, the same time it takes Jupiter to orbit once around the center of mass. Smaller planets like the Earth also cause perturbations on the Sun's orbit, but they are so tiny they couldn't be detected across interstellar distances. Analysis of the wobbles can give information about the planet's mass, orbit, period and distance from the star. If we make extremely detailed measurements of a star's position, accurate to one-thousandth of an arc second, we might be able to see wobbles in its motion due to a large unseen companion. Current techniques in astrometry , the branch of astronomy that deals with measuring positions of stars, are becoming capable of detecting Jupiter-sized planets around nearby stars.
Several stars do indeed seem to follow slightly wavy paths through space.
One problem is that the errors inherent in making the observations and measurements are about the same size as the planetary- induced wiggles astronomers are seeking, making it very difficult to be sure if a measured wobble is real. So far there have been no uncontested detections of planets from stellar wobbles. The Case of Barnard's Star Barnard's Star is a faint, red star about two-tenths as massive as the Sun. In 1963, Peter van de Kamp, then director of Swarthmore College's Sproul Observatory, announced that, based on an analysis of its motion, Barnard's Star had an unseen companion. Van de Kamp estimated that the companion was 50 percent heavier than Jupiter, much too small to be a star.