Longitude of the ascending node

right ascension of the ascending nodelongitude of ascending nodenodeRight Ascension of Ascending Nodeascending nodeAscending node longitudeline of nodesLOANlongitude of the ascending nodeslongitude of the node
The longitude of the ascending node (☊ or Ω) is one of the orbital elements used to specify the orbit of an object in space.wikipedia
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Orbital elements

orbital parametersorbital elementKeplerian elements
The Delaunay orbital elements, commonly referred to as Delaunay variables, are action-angle coordinates consisting of the argument of periapsis, the mean anomaly and the longitude of the ascending node, along with their conjugate momenta.

Plane of reference

reference planeplaneplanes
The two main orbital elements that are measured with respect to the plane of reference are the inclination and the longitude of the ascending node.

Nodal precession

precessnodes precessorbital precession
For a typical prograde orbit around Earth (that is, in the direction of primary body's rotation), the longitude of the ascending node decreases, that is the node precesses westward.

Non-inclined orbit

equatorial orbitequatorialEcliptic orbit
For non-inclined orbits (with inclination equal to zero), Ω is undefined.
As these orbits lack nodes, the ascending node is usually taken to lie in the reference direction (usually the vernal equinox), and thus the longitude of the ascending node is taken to be zero.

Orbital node

Nodeascending nodenodes
Here, n= is a vector pointing towards the ascending node.
This is done by specifying the longitude of the ascending node (or, sometimes, the longitude of the node.)

Binary star

spectroscopic binaryeclipsing binarybinary
In the case of a binary star known only from visual observations, it is not possible to tell which node is ascending and which is descending.

Earth

Earth's surfaceterrestrialworld

Clockwise

Heliocentric orbit

Heliocentrictrans-Mars injectionsolar orbit

Ecliptic

ecliptical orbitsecliptic planeplane of the ecliptic

Solar System

outer Solar Systeminner Solar Systemouter planets

Celestial pole

North Celestial Polesouth celestial polecelestial north pole

Orbital mechanics

astrodynamicsastrodynamicistorbital dynamics
In astrodynamics, the longitude of the ascending node can be calculated from the specific relative angular momentum vector h as follows:

Specific relative angular momentum

specific angular momentumangular momentum of planets and satellitesangular momentum per unit mass
In astrodynamics, the longitude of the ascending node can be calculated from the specific relative angular momentum vector h as follows:

Orbital inclination

inclinationinclinedtilted
For non-inclined orbits (with inclination equal to zero), Ω is undefined.

Equinox