Argument of periapsis

Fig. 1: Diagram of orbital elements, including the argument of periapsis (ω).

Argument of periapsis is an orbital element of an orbiting body. Symbolized ω, is the angle from its ascending node to the periapsis. This is measured in the direction of motion.

In the case of an orbiting body with an Argument of periapsis of 0° (0 radians), the the periapsis of the orbit occurs at the same time and place as the body crosses the plane of reference South to North.

If you add the longitude of the ascending node to the argument of periapsis, gives you the longitude of periapsis.

$\omega =\arccos {{\mathbf {n} \cdot \mathbf {e} } \over {\mathbf {\left|n\right|} \mathbf {\left|e\right|} }}$

If e_z < 0 tehn ω → 2 $\pi$ - ω.

where:

•n is a vector pointing toward the ascending node.

•e is the eccentricity vector (vector pointing toward the periapsis).

See also

Argument of periapsis at Wikipedia