Editing Orbital node (section)

== Node distinction ==
[[File:Planet orbit nodes 2 animation.gif|thumb|upright=1.1|Animation about nodes of two elliptic trajectories. (Click on image.)]]

If a reference direction from one side of the plane of reference to the other is defined, the two nodes can be distinguished. For geocentric and heliocentric orbits, the '''ascending node''' (or '''north node''') is where the orbiting object moves north through the plane of reference, and the '''descending node''' (or '''south node''') is where it moves south through the plane.<ref name="darlingasc">[http://www.daviddarling.info/encyclopedia/A/ascending_node.html ascending node], entry in ''The Encyclopedia of Astrobiology, Astronomy, and Spaceflight'', David Darling, on line, accessed May 17, 2007.</ref> In the case of objects outside the Solar System, the ascending node is the node where the orbiting secondary passes away from the observer, and the descending node is the node where it moves towards the observer.<ref>''The Binary Stars'', R. G. Aitken, New York: Semi-Centennial Publications of the University of California, 1918.</ref><sup>, p.&nbsp;137.</sup>

The position of the node may be used as one of a set of parameters, called ''[[orbital elements]]'', which describe the orbit. This is done by specifying the [[longitude of the ascending node]] (or, sometimes, the [[longitude of the node]].)

The '''line of nodes''' is the straight line resulting from the intersection of the object's orbital plane with the plane of reference; it passes through the two nodes.<ref name="darlinglon" />