Six parameters that can be used to define the path of a celestial body. The shape of the orbit is defined by its eccentricity (see conic) and semimajor axis. The orientation of the orbit is specified by the inclination of the orbital plane to the reference plane (usually the ecliptic) and by the longitude of the ascending node (the angular distance from the vernal equinox to the ascending node). The position of the body in its orbit is defined by its eccentric anomaly and the position as a function of time is calculated from the time of periapsis passage (see apsides).