Newtonian Theory of Orbit Perturbation and Revalued Mass of Sgr A*

It is a famous old problem: Why the orbit of the Moon around the Earth is stable under the condition that, calculated with F=GMm/R², the force of the Sun on the orbit is almost 2.2 times that of the Earth? We find, the calculated force of the Sgr A* on the orbit of the Oort cloud around the Sun is larger than that of the Sun; and, the force of the Sgr A* on the orbits on the edge of the ω Centauri is larger than that of the black hole at the center of the ω Centauri. It is known that the old problem about the Moon around the Earth can be understood with the Newtonian theory of orbit perturbation. Here, we find, the problem about the Oort cloud and the ω Centauri also can be understood with the Newtonian theory of orbit perturbation. And, we conclude that the mass of the Sgr A* should be M_SgrA*∼1.8×10¹¹M_Sun ; and, at the center of every stellar cluster there should be a black hole or other massive body which can be easily measured with any one of the orbits in the cluster or with the Hill sphere.