Celestial mechanics, definition and study. A-Z index of Cognitio.

Celestial mechanics is the branch of classical mechanics that studies the motion of celestial bodies, in particular planets, natural and artificial satellites, asteroids and comets from a physical-mathematical point of view.

Asteroid, definition and study. A-Z index of Cognitio.


The main problem of celestial mechanics concerns the stability of the Solar System.

Solar system, definition and study. A-Z Index of Cognitio.

Solar system

This problem can be tackled through mathematical techniques, known as “perturbation theory”. Other problems of interest to celestial mechanics are the orbital resonances, the interactions between revolution and rotation, the dynamics of asteroids and Kuiper objects, the determination of the orbits of extra-solar planetary systems.

Extrasolar planet, definition and study. A-Z index of Cognitio.

Extrasolar planet

The scientific treatment of celestial mechanics began with Isaac Newton, who introduced the law of universal gravitation in the Principia work of 1687.

Gravitational interaction, definition and study. A-Z index of Cognitio.

Gravitational interaction

He proposed the term “rational mechanics” for the study of the motion of celestial bodies. Over one hundred years later it was Pierre-Simon Laplace who introduced the name “celestial mechanics”. The bodies of the solar system have been observed for four centuries with great accuracy by astronomers. The mutual interactions of these bodies, mainly gravitational, give rise to motions also very complex and difficult to predict the degree of precision required by the observations. The position of the Moon is known for example with an error of about ten centimeters thanks to the laser ranging technique.

The discovery of Neptune in 1871 was made possible by the prediction of his position in the sky made “in tip of pen” – that is, with mathematical calculations. Today the chaos theory unveils the origin and evolution of many bodies of the Solar System that have remained shrouded in mystery for centuries. The advent of the space age and the need for the probes to travel on trajectories that save time and fuel, has multiplied the potential of celestial mechanics by differentiating its tools and objectives. Modern celestial mechanics allow us to study the link between the long-term climate changes on our planet and those of its orbit around the Sun, as well as to adequately address the problem of space debris that risks making the circumterrestrial space impracticable.

Sun, definition and study. A-Z index of Cognitio.


It is no coincidence that the term “resonance” indicates the establishment of particular “harmonies” that lead two or more celestial bodies to draw very particular geometries in the sky. The most recent case is that of asteroid 2016 HO3, which has a period of revolution around the Sun equal to that of the Earth (technically called “resonance 1: 1”) but a slightly eccentric orbit.

Earth origins, definition and study. A-Z index of Cognitio.

Earth origins

The result is that 2016 HO3 never gets too far from our planet, in fact, it turns around us like a distant satellite. But it is not the attraction of the Earth that makes it move, but a “trick” of celestial mechanics, the result of the different speed with which an eccentric orbit is traversed. A bit like when on the highway we come across a driver who first overcomes us and then slows down, forcing us, we who instead proceed at constant speed, to overcome it again … and so on. So for astronomers 2016 HO3 is a “micro-satellite”, a temporary travel companion that sooner or later (it was calculated in a few centuries), coming out of the resonance will go on its way. The discovery of 2016 HO3 has made a bell ring in the head of many celestial mechanics: is not it the ideal solution to turn around a body in space without too many complications? Possible that no one has thought of it before? It turns out then that trajectories of this type (called “fly around” case) are used for years to inspect the exterior of the International Space Station – allowing astronauts to shoot spectacular, pure science fiction.

Cosmic space, definition and study. A-Z index of Cognitio.

Cosmic space

And again: a similar orbital configuration will allow you to “park” near the Moon the large boulder taken from the surface of an asteroid during the ARM mission (Asteroid Redirect Mission) currently under study at NASA, without running the risk that there falls on the head.

NASA looks to the exploration of asteroids. Original article by Alessandro Brizzi.


They are then referred to as “Cis-lunar orbits” or with the acronym DRO (Distant Retrograde Orbits). In reality, they are variations on the theme of the same concept, which, in the scientific literature, had been formulated more than forty years ago by a great celestial mechanic: the Frenchman Michel Henon. 

Celestial mechanics, definition and study. A-Z index of Cognitio.



To open the video  click on the image, good view from your Alessandro Brizzi.

Celestial mechanics, definition and study. A-Z index of Cognitio.

Celestial mechanics