# Longitude of the ascending node

The argument of the node is in the celestial mechanics of the angle from the coordinate origin of the reference plane to the ascending node. For the argument of the node is for traditional reasons the term node length or spring angle use. "Length" refers here but generally the first polar coordinate of a Spherical coordinate system.

The argument of the node is one of the six orbital elements, which for adequate description of a - perfect - meet Kepler track and is almost always denoted by Ω. Along with the inclination and the argument of the periapsis it defines the position of the web plane in the space. It corresponds to the Euler angle ψ of the general position calculation for arbitrary orientation ( angular position ) of objects in three-dimensional space.

Depending on the nature of the object, the path is specified, the following four levels are common:

- The ecliptic solar orbital solar system objects: planets, asteroids, comets. The argument of the node is the ecliptic longitude, which is the angle measured from the vernal equinox (English longitude of the ascending node LOAN ).

- The argument of the ascending node Ω, and right ascension of the ascending node or RAAN (english right ascension of the ascending node ) is then the right ascension along the Earth's equator with respect to the vernal equinox.

- The argument of the node, the angle along the main object with respect to the equatorial plane of a certain reference point.

- The argument of the node is the angle to the celestial pole

In the case of Kepler orbits (only two bodies in a vacuum) is the argument of the node constant and the orbital plane remains in its alignment with the fixed stars stable. In gravitational third-body perturbations, the argument of the node suffers small partially periodic changes. Therefore, the path element is specified as a series oskulierender terms with respect to a period, so as at any given time valid approximate solution.

As a first approximation, as the value for the argument of the lunar node to

The approximately 1934 ° in 100 Julian years ( 365.35 days to ) correspond to a complete revolution of the line of nodes in 18.61 years, the nutation.