Editing Orbital elements (section)

=== Rotation describing elements ===
[[File:Orbit1.svg|thumb|In this diagram, the [[Orbital plane (astronomy)|orbital plane]] (yellow) intersects a reference plane (gray). For Earth-orbiting satellites, the reference plane is usually the Earth's equatorial plane, and for satellites in solar orbits it is the [[Plane of the ecliptic|ecliptic plane]]. The intersection is called the [[Orbital node|line of nodes]], as it connects the reference body (the primary) with the ascending and descending nodes. The reference body and the [[vernal point]] (<big>♈︎</big>) establish a reference direction and, together with the reference plane, they establish a reference frame.]]
Three parameters are required to describe the orientation of the plane of the orbit, and the orientation of the orbit within that plane.

* [[Inclination]] (''{{mvar|i}}'') — vertical tilt of the ellipse with respect to the reference plane, typically the [[equator]] of the central body, measured at the [[ascending node]] (where the orbit passes crosses the reference plane, represented by the green angle ''{{mvar|i}}'' in the diagram). Inclinations near zero indicate [[Near-equatorial orbit|equatorial orbits]], and inclinations near 90° indicate [[polar orbit]]s. Inclinations from 90 to 180° are typically used to denote [[Retrograde and prograde motion|retrograde orbits]].
* [[Longitude of the ascending node]] ({{Math|Ω}}) — describes the angle from the [[ascending node]] of the orbit ({{math|☊}} in the diagram) to the reference frame's reference direction (♈︎ in the diagram). This is measured in the reference plane, and is shown as the green angle {{Math|Ω}} in the diagram. This quantity is undefined for perfectly equatorial (coplanar) orbits, but is often set to zero instead by convention.<ref name=":02" /> This quantity is also sometimes referred to as the right ascension of the ascending node (or RAAN).
* [[Argument of periapsis]] (''{{mvar|ω}}'') — defines the orientation of the ellipse in the orbital plane, as an angle measured from the ascending node to the periapsis (the closest point the satellite body comes to the primary body around which it orbits), the purple angle ''{{mvar|ω}}'' in the diagram. This quantity is undefined for circular orbits, but is often set to zero instead by convention.<ref name=":02" />

These three elements together can be described as [[Euler angles]] defining the orientation of the orbit relative to the reference coordinate system. Although these three are the most common, other elements do exist, and are useful to describe other properties of the orbit.

* [[Longitude of periapsis]] ({{Mvar|ϖ}}) — describes the angle between the vernal point and the periapsis, measured in the reference plane. This can be described as the sum of the longitude of the ascending node and the argument of periapsis: <math>\varpi=\Omega+\omega</math>. Unlike the longitude of the ascending node, this value is defined for orbits where the inclination is zero.