Editing Equatorial bulge (section)

== Effect on satellite orbits ==
The fact that the Earth's gravitational field slightly deviates from being spherically symmetrical also affects the orbits of [[satellite]]s through [[ Secular variation | secular ]] orbital precessions.<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
|arxiv = 1107.2916
|issue=12
|pages=124001
|bibcode=2011PhRvD..84l4001I
 |doi=10.1103/PhysRevD.84.124001
 |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 depend on the orientation of the Earth's symmetry axis in the inertial space, and, in the general case, affect ''all'' the Keplerian [[orbital elements]] with the exception of the [[semimajor axis]]. If the reference ''z'' axis of the coordinate system adopted is aligned along the Earth's symmetry axis, then only the [[longitude of the ascending node]] Ω, the [[argument of pericenter]] ω and the [[mean anomaly]] ''M'' undergo secular precessions.<ref>{{cite journal 
|last1=King-Hele
|first1=D. G.
|date=1961
|title=The Earth's Gravitational Potential, deduced from the Orbits of Artificial Satellites
|journal=[[Geophysical Journal]]
 |volume=4
|issue=1
|pages=3–16
|bibcode=1961GeoJ....4....3K
 |doi=10.1111/j.1365-246X.1961.tb06801.x
 |doi-access=free
}}</ref>

Such perturbations, which were earlier used to map the Earth's gravitational field from space,<ref>{{cite journal 
|last1=King-Hele
|first1=D. G.
|date=1983
|title=Geophysical researches with the orbits of the first satellites
|journal=[[Geophysical Journal]]
 |volume=74
|issue=1
|pages=7–23
|bibcode=1983GeoJ...74....7K
 |doi=10.1111/j.1365-246X.1983.tb01868.x
 |doi-access=free
}}</ref> may play a relevant disturbing role when satellites are used to make tests of [[general relativity]]<ref>{{cite journal 
|last1=Renzetti
|first1=G.
|date=2012
|title=Are higher degree even zonals really harmful for the LARES/LAGEOS frame-dragging experiment?
|journal=[[Canadian Journal of Physics]]
 |volume=90
|issue=9
|pages=883–888
|bibcode=2012CaJPh..90..883R
 |doi=10.1139/p2012-081
 }}</ref> because the much smaller relativistic effects are qualitatively indistinguishable from the oblateness-driven disturbances.