Earth is the third planet of the star Sol.
From the initial observations of planets now visited by the newly formed Planetary League of the Ancients, it seems apparent that sample groups of many of Earth major cultural groups are to be found on various planets of relatively nearby stars, perhaps to observe over the millennia how societies evolve without the contamination of other cultures and languages.
Earth, or Terra as it is called on the official records of the League, is the third of the five charter members, along with Arran, Daga, Mars, and Sukunka, of Cor (Procyon).
Most of the people of Earth, however, know nothing of the Planetary League and many scientists and government agencies continue to try to disprove the likelihood of interstellar travel.
This is the home world of all the men of Arran, including Oriana's father, Angus, as well as many other characters in the stories.