^Roger R. Bate, Donald D. Mueller, Jerry E. White, "Fundamentals of astrodynamics"（Dover Publications, 1971）, e.g. at ch.9, p.385.
^牛頓在1684年寫道："By reason of the deviation of the Sun from the center of gravity, the centripetal force does not always tend to that immobile center, and hence the planets neither move exactly in ellipses nor revolve twice in the same orbit. Each time a planet revolves it traces a fresh orbit, as in the motion of the Moon, and each orbit depends on the combined motions of all the planets, not to mention the action of all these on each other. But to consider simultaneously all these causes of motion and to define these motions by exact laws admitting of easy calculation exceeds, if I am not mistaken, the force of any human mind."（quoted by Prof G E Smith （Tufts University）, in "Three Lectures on the Role of Theory in Science"[永久失效連結] 1. Closing the loop: Testing Newtonian Gravity, Then and Now); and Prof R F Egerton（Portland State University, Oregon）after quoting the same passage from Newton concluded: "Here, Newton identifies the "many body problem" which remains unsolved analytically." （页面存档备份，存于互联网档案馆）
^Roger R. Bate, Donald D. Mueller, Jerry E. White, "Fundamentals of astrodynamics"（Dover Publications, 1971）, e.g. at p.387 and at section 9.4.3, p.410.
