Budget vacations for Comets that cease reacting to the Sun may be either dormant that is, generally inactive, but occasionally laring into life for a limited period when some of their volatiles are freshly exposed or extinct that is, devoid of volatiles and therefore never reacting to the Sun. Comet Encke, with its orbital period of years, burst to life in , but scholars have been unable to ind a single reference to it in the historical records stretching back over two millennia, most likely because it was dormant most, if not all, of that time. The comet is now, it would seem, in the last decades of its current phase of activity. It should also be noted that, due to fragmentation, each Jupiter-family comet is probably little more than a small kernel of a larger original progenitor comet. Orbital Elements The orbit of a comet at any particular point in time, and therefore its place within the dome of the sky, may be fully known if we have six pieces of technical information, known as the orbital elements. The six elements are the closest distance that the object comes to the Sun perihelion distance in AU q and the time when this occurs T, the eccentricity e of the cometary orbit, the inclination of the plane of that orbit relative to the plane of the ecliptic i, the point where the cometary orbit crosses the plane of the ecliptic as the comet moves from the south to the north the longitude of the ascending node and the angular distance from there to the perihelion point the argument of perihelion ?. FIG The orbital elements of a comet. Budget vacations 2016.