elements of the orbit

Even in his swashbuckling adventure stories, Anderson is famous for beginning with calculations of the elements of the orbit of the world to be his setting.

One may similarly define the stabilizer of an orbit (the subgroup that fixes all elements of the orbit) and the corresponding field of moduli of the orbit, another invariant of the dessin.

From this projected ellipse the complete elements of the orbit may be computed, where the semi-major axis can only be expressed in angular units unless the stellar parallax, and hence the distance, of the system is known.