Kepler S Laws Quotes

“Kepler's laws, although not rigidly true, are sufficiently near to the truth to have led to the discovery of the law of attraction of the bodies of the solar system. The deviation from complete accuracy is due to the facts, that the planets are not of inappreciable mass, that, in consequence, they disturb each other's orbits about the Sun, and, by their action on the Sun itself, cause the periodic time of each to be shorter than if the Sun were a fixed body, in the subduplicate ratio of the mass of the Sun to the sum of the masses of the Sun and Planet; these errors are appreciable although very small, since the mass of the largest of the planets, Jupiter, is less than 1/1000th of the Sun's mass.”
― Isaac Newton, The Principia : Mathematical Principles of Natural Philosophy

“[...] The movement of the celestial bodies can be given as an example. It is not exactly circular, but elliptic; the ellipse constitutes as it were a first “specification” of the circle, by the splitting of the center into two poles or “foci” in the direction of one of the diameters which thereafter plays a special “axial” part, while at the same time all the other diameters are differentiated one from another in respect of their lengths. It may be added incidentally in this connection that, since the planets describe ellipses of which the sun occupies one of the foci, the question arises as to what the other focus corresponds to; as there is nothing corporeal actually there, there must be something belonging only to the subtle order; but that question cannot be further examined here, as it would be quite outside our subject.”
― René Guénon, The Reign of Quantity & the Signs of the Times