IVOA Catalogue Data Model

3.4.3.3 Orbit.aphelionMaximum distance from a reference point along the orbit3.4.3.4 Orbit.inclinationAngle between the line-of-sight to the source and the normal to the planecontaining the orbit3.4.3.5 Orbit.eccentricityFraction of the distance along the semi-major axis at which the focus lies (e=c/a,where c is the distance from the center of the conic section to the focus and a isthe semi-major axis)3.4.3.6 Orbit.positionAngleApparent position angle of the orbit on the sky vault3.4.3.7 Orbit.periodOrbital period