Orbital elements. The elements of the elliptical orbit of a planet or comet around the Sun: (N) Ascending node, (°), First Point of Area.

A set of parameters that together completely define the shape, orientation and timing of orbital motion. Those most commonly used for the orbits of planets and comets around the Sun are semimajor axis, perihelion distance, eccentricity, inclination, argument of perihelion, longitude of the ascending node and period. In order to determine the position of an object at a specific time, it is also necessary to know the time when a particular point in the orbit is reached, such as perihelion passage. Analogous elements are used to describe the orbits of stars in binary systems or of satellites (natural or artificial) orbiting planets.
The standard orbital elements are detailed in the table and the illustration, which depicts an elliptical orbit in the solar system. Here P is the perihelion point, N the ascending node and the direction of the First Point of Aries.

Name	Symbol	Function
Semimajor axis	a	Defines the size of an elliptical orbit
Minimum distance from interferometer pericentre	q	Defines the size of a parabolic or hyperbolic orbit
Eccentricity	e	Defines the distance of the foci from the centre for an elliptical orbit
Inclination	i	Angle between the orbital plane and the reference plane
Longitude of the ascending node	W	Direction in space of the line where the orbit intersects the reference plane
Argument of pericentre	w	Defines the orientation of the orbit with respect to the reference plane
Period	P	Time to complete one revolution of a closed orbit
Time of pericentre passage	T	Sets the time frame of the orbital motion.