Why the shape of the orbit ellipse?
Your English is fine. The gravitational attraction is not inherently variable, although the effect does decrease with the square of the distance. You may be thinking that orbits should be circular. An idealized form of an ellipse is in fact circular. So if everything was in perfect order as the planets were forming, then the orbits would perhaps be circular. But that was not the case – as usual. The planets formed from clouds of matter that were sort of randomly spinning around the sun to begin with. It would have been quite unusual if those imperfect clouds of debris had just happened to collect perfectly evenly to form perfectly circular orbits. Instead, they collected in sort of an imperfect manner to result in imperfect, elliptical orbits. Kepler showed that the equations work just as well for an ellipse as they do for a circle. In fact (as I already mentioned) a circle is just an ellipse that happens to be symmetric. Remember that the planets move slower as they move farther away
