### Keplerian orbit

**(Kepler orbit, osculating orbit)**
(orbit following a perfect ellipse or other conic section)

A **Keplerian orbit** (or **Kepler orbit**) is an **orbit**
(path of an astronomical object gravitationally bound
to another, particularly, a repeating pattern)
that follows a perfect **ellipse**, **parabola**, or **hyperbola**
(i.e., conic section).
This is the case for a point mass
orbiting another point mass with no other mass near
enough to affect them, i.e., an orbit maintained purely by the gravitation
between two points (or spherically-symmetric objects).
Planets and stars often approximate the behavior of point masses,
for approximating spheres whose shells each have its
mass distributed homogeneously (spherically symmetric):
such spheres act like point masses.
Orbits diverge from Keplerian due to additional mass,
such as another planet near enough to affect its orbit,
and/or a planet's divergence from the even distribution of mass
described above, such as having a region near the surface
that is especially massive.

Such an orbit maintained solely to gravitational interaction also
has a particular orbital speed related to the masses and distance,
distance between them and shape of the orbit (**Keplerian speed**).
An orbit may be described as faster or slower than *Keplerian* if
factors other than gravity are contributing, though it still may
be in the shape of a Keplerian orbit.

The term **osculating orbit** is essentially a synonym for
*Keplerian orbit*, most commonly used to describe the theoretical
orbit a particular object would have if it were not for sources of
perturbation such as other bodies, tidal forces,
radiation pressure, etc.

(*dynamics,orbits*)
**Further reading:**

http://en.wikipedia.org/wiki/Kepler_orbit

**Referenced by pages:**

barrier

celestial mechanics

corotation torque

radial-drift barrier

epicycle

Keplerian disk

Kepler radius

mean anomaly

Poynting-Robertson effect

radial drift

rotation curve

streaming instability

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