A non-inclined orbit is an orbit which is contained in the plane of reference. The inclination is 0 for prograde orbits, and π (180°) for retrograde orbits. If the plane of reference is the equator, these orbits are called equatorial; if the plane of reference is the ecliptic, they are called ecliptic. As these orbits lack nodes, the ascending node is usually taken to lie in the reference direction (usually the vernal equinox), and thus the longitude of the ascending node is taken to be zero. Also, the argument of periapsis is undefined.
Famous quotes containing the word orbit:
“The Fitchburg Railroad touches the pond about a hundred rods south of where I dwell. I usually go to the village along its causeway, and am, as it were, related to society by this link. The men on the freight trains, who go over the whole length of the road, bow to me as to an old acquaintance, they pass me so often, and apparently they take me for an employee; and so I am. I too would fain be a track-repairer somewhere in the orbit of the earth.”
—Henry David Thoreau (1817–1862)