longitude of the periapsis

Adding the argument of periapsis to the longitude of the ascending node gives the longitude of the periapsis.

Orbital parameters that are used to describe the relation of co-orbital objects are the longitude of the periapsis difference and the mean longitude difference.

Astronomers commonly express the timing of perihelion relative to the vernal equinox not in terms of days and hours, but rather as an angle of orbital displacement, the so-called longitude of the periapsis.

The longitude of the periapsis is the sum of the mean longitude and the mean anomaly ( ) and the mean longitude of the sum of the longitude of the ascending node and the argument of periapsis ( ).