# Eccentricity vector

In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.wikipedia

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### Kepler orbit

**Keplerian orbitKeplerianKeplerian ellipse**

In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.

For a "close to circular" orbit the concept "eccentricity vector" defined as is useful.

### Osculating orbit

**osculatingnon-Keplerianosculating elements**

Its main use is in the analysis of almost circular orbits, as perturbing (non-Keplerian) forces on an actual orbit will cause the osculating eccentricity vector to change continuously.

### Laplace–Runge–Lenz vector

**Runge–Lenz vectorelsewhereLaplace-Runge-Lenz vector**

The LRL vector has been re-discovered several times and is also equivalent to the dimensionless eccentricity vector of celestial mechanics.

### Orbital eccentricity

**eccentricityeccentriceccentricities**

In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.

The eccentricity of an orbit can be calculated from the orbital state vectors as the magnitude of the eccentricity vector:

### Argument of periapsis

**argument of perihelionargument of perigeeargument of pericenter**

For the eccentricity and argument of periapsis parameters, eccentricity zero (circular orbit) corresponds to a singularity.

### Celestial mechanics

**celestialcelestial dynamicscelestial mechanician**

In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity.

### Dimensionless quantity

**dimensionlessdimensionless numberdimensionless quantities**

### Euclidean vector

**vectorvectorsvector addition**

### Apsis

**perigeeperihelionapogee**

### Specific relative angular momentum

**specific angular momentumangular momentum of planets and satellitesangular momentum per unit mass**

### Position (vector)

**positionposition vectorposition vectors**

### Standard gravitational parameter

**gravitational parametergeocentric gravitational constantheliocentric gravitational constant**

### Orbit

**orbitsorbital motionplanetary motion**

### Apse line

**line of apsesline of apsidesline-of-apsides**

An apse line, or line of apsides, is an imaginary line defined by an orbit's eccentricity vector.

### Eccentricity

**eccentriceccentricallyEccentricity (disambiguation)**

### Frozen orbit

**frozenJ3 perturbationneeded an inclination of 63.4°**

The perturbing force caused by the oblateness of the Earth will in general perturb not only the orbital plane but also the eccentricity vector of the orbit.

### Perifocal coordinate system

Perifocal reference frames are most commonly used with elliptical orbits for the reason that the coordinate must be aligned with the eccentricity vector.

### Eccentricity (mathematics)

**eccentricityeccentriceccentricities**