From The Stargate Omnipedia
Planet in a distant galaxy, inhabited by the descendants of the Alterans
Celestis is the location of Ver Eger, a village populated by humans who worship the Ori.
The Plains of Celestis is the location of the city of Celestis, home of the Doci and the Flames of Enlightenment where the Ori reside.
HOME TO - Ver Egens, Doci, Ori
FIRST APPEARED - Avalon, Part 2
Avalon, Part 2 - Daniel and Vala enter the bodies of Harrid and Sallis, inhabitants of Celestis.
Origin - Daniel and Vala are taken to the Plains of Celestis from Ver Eger to have a face-to-face meeting with the Doci and the Ori themselves.