Freedman and Kaufmann
An extrasolar planet is one that
orbits a star other than our Sun.
Every extrasolar planet around a Sun-like star has
been found (or confirmed) using the
Doppler shift radial velocity technique.
Freedman and Kaufmann
This occurs because of the Universal Law of Gravity!
Just as the star pulls on the planet, so does the planet
pull on the star.
Demo: both orientations, with axis
parallel and perpendicular to line of sight!