Ptero is one of the moons of Ida where all the inhabitants of Xanth, all the characters that might inhabit Xanth, and characters who are just mere ideas in others heads. The inhabitants of Ptero who also have a likeness on Xanth have all of the memories of their Xanth likeness except the memories occurring on their "off-year", the year currently being lived by their Xanth character on Xanth. Traveling east or west depends on a person's age. One can not travel outside of their lifetimes. So one can go only so far green until their birth, and one can go only so far yellow until their death.