Editing Orbit (section)

===Oblateness===
The standard analysis of orbiting bodies assumes that all bodies consist of uniform spheres, or more generally, concentric shells each of uniform density. It can be shown that such bodies are gravitationally equivalent to point sources.

However, in the real world, many bodies rotate, and this introduces [[oblateness]] and distorts the gravity field, and gives a [[Quadropole#Gravitational quadrupole|quadrupole]] moment to the gravitational field which is significant at distances comparable to the radius of the body. In the general case, the gravitational potential of a rotating body such as, e.g., a planet is usually expanded in multipoles accounting for the departures of it from spherical symmetry. From the point of view of satellite dynamics, of particular relevance are the so-called even zonal harmonic coefficients, or even zonals, since they induce secular orbital perturbations which are cumulative over time spans longer than the orbital period.<ref>{{cite journal
|last1=Iorio
|first1=L.
|date=2011
|title=Perturbed stellar motions around the rotating black hole in Sgr A* for a generic orientation of its spin axis
|journal=[[Physical Review D]]
 |volume=84
|issue=12
|pages=124001
|bibcode=2011PhRvD..84l4001I
 |doi=10.1103/PhysRevD.84.124001
 |arxiv = 1107.2916 |s2cid=118305813
}}</ref><ref>{{cite journal
|last1=Renzetti
|first1=G.
|date=2013
|title=Satellite Orbital Precessions Caused by the Octupolar Mass Moment of a Non-Spherical Body Arbitrarily Oriented in Space
|journal=[[Journal of Astrophysics and Astronomy]]
 |volume=34
|issue=4
|pages=341–348
|bibcode=2013JApA...34..341R
 |doi=10.1007/s12036-013-9186-4
 |s2cid=120030309
}}</ref><ref>{{cite journal
|last1=Renzetti
|first1=G.
|date=2014
|title=Satellite orbital precessions caused by the first odd zonal J3 multipole of a non-spherical body arbitrarily oriented in space
|journal=[[Astrophysics and Space Science]]
 |volume=352
|issue=2
|pages=493–496
|bibcode=2014Ap&SS.352..493R
 |doi=10.1007/s10509-014-1915-x
 |s2cid=119537102
}}</ref> They do depend on the orientation of the body's symmetry axis in the space, affecting, in general, the whole orbit, with the exception of the semimajor axis.