The newest addition to the standard chart, and the least settled.
Chiron crosses Saturn's orbit at one end and Uranus's at the other, which makes its orbit unstable on a scale of a million years or so. It is neither an asteroid nor a comet in the usual sense.
Its eccentric orbit means very uneven time per sign — under two years in Aries, nearly eight in Libra.
Computing it requires the asteroid ephemeris files rather than the planetary ones. If those are missing, Swiss Ephemeris silently falls back and Chiron is the first thing to go wrong.
What it is
A centaur — a small icy body on an unstable orbit between Saturn and Uranus. Discovered 1977.