Gravity and the planets’ orbits

Most of the bodies of the Solar System revolve around the Sun in orbits that are not circular but elliptical and in which the Sun occupies one of the two foci (Kepler’s First Law). In particular, planets move along orbits that are slightly eccentric, i.e. slightly squashed, and almost all on the same plane because of the mechanism with which they were created during the formation of our planetary system. Dwarf planets and minor bodies on the contrary are characterised by more elongated and inclined orbits.
All bodies in the Solar System move at different speeds depending on their distance from the Sun; faster when they are closer to the star, and slower when they are further away (Kepler’s Second Law).
Moreover, as the distance increases so does the length of time taken to complete a revolution around the Sun (Kepler’s Third Law); in fact, Mercury takes only 88 days while Neptune takes nearly 165 years.
The great force that keeps the Solar System together and prevents the single components from dispersing into space is gravity, a force generated by bodies simply because they have a mass. In fact, between any two bodies there exists a force of mutual attraction that is directly proportional to the product of their respective masses and inversely proportional to the square of the distance between them. Due to its mass, the Sun is the body that has the greatest gravitational influence on all the other components of the system that revolve around it; and following the same principle, satellites revolve around their parent planet. But planets influence each other too and influence the movement of minor bodies, even though this effect is greatly inferior to that of the Sun on each of them. For example, Neptune was discovered because Uranus’s orbit was different from the predictions made on the basis of mathematical calculations; this difference was generated just by the gravitational pull of the outermost of the giant planets in the Solar System.
The orbits of the bodies in the Kuiper Belt are always disturbed by Neptune’s gravitational force just as the asteroids within the main belt feel Jupiter’s gravitational attraction. On Earth, the gravity of other bodies generates very different phenomena which are more or less well known to us; it is worth mentioning, for example, the ocean tides and the precession of the equinoxes, a long term variation of the inclination of the rotational axis.

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