(todo)
“Just as Newton left out all consideration of the equal and opposite reaction to the attraction of gravitation, which is the repulsion of radiation, so does Kepler leave the other focus of his ellipses out of his consideration. “The sun is one of the foci of planetary elliptical paths,” he says; but how about the other one? My friendly critics will of course admit that there are two foci to any elliptical orbit. If one of these foci is important, why is not the other equally so? What is the cause of elliptical orbits if not that some doubly acting force, concentrated at two foci, is exerting its opposite influences on both masses, not on one. For this reason also it is inaccurate, because untrue, to say that the sun is at one of its foci. That informs that the sun's centre is one of its foci, which is not true. The true focus, which only happens to be within the sun, because of the sun's huge bulk, is the mutual gravitative centre of both sun and planet, or earth and moon. If a planet happened to be a big fellow, the focus referred to would be a long way outside of the sun.(…) The neglected focus is the mutual centre of repulsion which is the lowest point in the pressure gradient between any two masses. These two oppositely acting foci are the controls which determine the orbits of both masses around each other instead of one mass around the other, which was the apparent limit of Kepler's consideration.” - Walter Russell
(todo: supernova (gas buildup ignition), pulsars (remnant star motion flux), quasars, ring galaxies, … )