Schematic illustration of the tidal acceleration exerted by a planet of mass m on a point x in the solar interior. O represents the center of mass of the solar system. O_b represents the solar center of mass. x_b is the instantaneous position of the solar center of mass with respect to the center of mass of the solar system. The vector r represents the instantaneous distance between the planet and the solar center of mass.  { u_i }  is the basis of the equator J2000 reference frame (explained in text). The dashed blue lines represent the boundaries of the solar tachocline, which are assumed to be ellipsoids.