[en] It is shown that the external gravitational field of a nonstatic spherically symmetric body is static in the relativistic theory of gravitation. In the general theory of relativity it is shown that the graviational field exterior to a nonstatic spherically symmetric body reduces to a static gravitational field given by the Schwarzschild metric (Birkhoff's theorem). However, the Schwarzschild solution does not satisfy the equations of the relativistic theory of gravitation, and it is therefore necessary to prove the analogous theorem in the latter theory