III. Orbits

It has been shown by others that orbiting bodies follow an elliptical shaped (not egg shaped) orbit about the more massive body. In the early era of astronomy it was thought that the orbits were circular, as that was regarded as being more "perfect". Indeed, as a first approximation the orbits are very nearly circular – with a few exceptions. The circular approximation is sufficient for the purposes of the work accomplished in Project Jupiter because of the limitations of separation measuring equipment available to most amateurs.

In the vastness of space, there is no "up" or "down", or preferred direction. As such, the plane of the orbit of bodies may be at any angle to the observer. In double star work that is especially true, so the observed orbits may be viewed as if an observer were perpendicular to the orbit, nearly in the plane of the orbit, or in between those positions. The differing perspective distorts the perceived shape of the elliptical orbit. Fortunately for Project Jupiter the plane of the orbits of Jupiter’s moons are such that the orbit characteristics may be determined with relative ease.