This is the second number that aligns the orbit ellipse in space. The intersection of the orbit plane and the equatorial plane is called the lines of nodes. The point where the satellite's orbit crosses the equator going south to north is called the ascending node. The one on the opposite side of the Earth, where the satellite passes into the Southern Hemisphere is called the descending node. Since the orbit is fixed relative to the stars and not to the surface of the Earth, the astronomical coordinate system of right ascension and declination is needed to measure the position of the ascending node.
Declination is the angle measured up from the equatorial plane, just like inclination.
Now that we have oriented the orbital plane in space, we need to determine the position of the orbital ellipse in the orbital plane, using the angle called the argument of perigee. The rest of the elements deal with the shape and position of the orbit in the orbital plane. This restricts the problem to the stylized orbit. The perigee is the point on the orbit that satellite is closest to the Earth. On the opposite side of the orbit, the satellite is at its farthest point from the Earth called the apogee.