ABSTRACT
A linear theory for the heat conduction in a spherical, solid and rotating body illuminated by solar radiation is developed. The recoil force due to the thermally re-emitted radiation by the surface of the body is computed, including all the terms depending both on the body's rotation frequency and the mean motion of its revolution about the Sun. The present solution thus overcomes a drawback of the previous approaches, which have been tailored separately either to the diurnal or to the seasonal variant of the so--called Yarkovsky effect, corresponding to different limiting cases of the current theory. We pay a special attention to compute the secular effects on the semimajor axis of the body's orbit about the Sun. The results from the general model coincide with those of the previous approaches to a high level of accuracy, as the relative size of the additional ``mixed'' terms is smaller than $10^{-3}$ for plausible parameter choices. This confirms that the use of the simplified formul{\ae} is warranted in the relevant Solar System applications.