Oa

Oa is a fictional planet that lies at the center of the DC Comics universe. Since its inception, Oa has been the planetary citadel of the Guardians of the Universe and the headquarters of the Green Lantern Corps. It first appeared in Green Lantern vol 2 #1, when the Guardians summoned Hal's 'energy duplicate' so they could hear of his origin.

History
One of the oldest planets in the universe, Oa serves as the home and headquarters for a race of blue-skinned powerful humanoids who have dubbed themselves the Guardians of the Universe. The Guardians administer the Green Lantern Corps, a group of powerful universal police officers equipped by the Guardians with green-colored power rings along with green lanterns with which to charge the rings. According to the story "Heart of a Star" in the Sandman: Endless Nights graphic novel, Oa's star is called Sto-Oa (the Light of Oa) by the children of the planet's inhabitants. Its location has been firmly established by numerous references in Green Lantern comics over the years. It was formerly the center of the universe until the events of Infinite Crisis.

Oa's history is not clear; according to some stories, the Guardians originated on a planet called Maltus. These evolved Maltusians later moved to Oa and named themselves Oans. Oa became a convenient base of operations. Other stories had the Oans living there from the beginning.

Oa appears as a desert-like, lifeless planet. The main feature is the Guardians' city. Green Lantern Corps member Hal Jordan, the Green Lantern of sector 2814 (which includes Earth), under the influence of the evil entity Parallax, kills all but one of the Guardians and most of the Corps before draining Oa's Central Power Battery of its energy. During the Circle of Fire event, what remains of the planet served as a base of operations for the villain Oblivion.

The planet is reformed sometime later by Jordan's old friend and associate Tom "Pie-Face" Kalmaku in the graphic novel Legacy: The Last Will and Testament of Hal Jordan. The Central Power Battery is later recharged and the Guardians resurrected shortly thereafter by Kyle Rayner after he spends some time as the near-omnipotent "Ion".

After attacks by Superboy-Prime and the Spider Guild, the Guardians fortify Oa by creating a planetwide armor and defensive system to prevent attacks. The full capability of the new systems is still unknown. They were not, however, enough to prevent an assault by the Sinestro Corps, which resulted in the deaths of many Green Lanterns. Afterward, the Corps doubled its defenses. However, a rogue Guardian, Scar, weakened its defenses for an attack from the Black Lantern Corps.

It is revealed in Final Crisis: Legion of 3 Worlds that Sodam Yat is the last Guardian of the Universe in the 31st century, while Rond Vidar is the last remaining Green Lantern until he is killed by Superboy-Prime's Legion of Super-Villains. Oa lies mostly in ruins, the power battery cracked, and the rings of the Corps lie in a pile, unable to locate new bearers due to the apparent death of Mogo. Statues of legendary Green Lantern Corps members, including Hal Jordan, Guy Gardner, John Stewart, Kyle Rayner, Arisia, and Ch'p, line the hall where the Guardians formerly met.

Green Lanterns Corps Headquarters

 * Dining Hall: The dining hall can accommodate any Green Lantern's nutritional needs. The executive chef, Greet, specializes in replicating dishes from across the universe. He, unfortunately, has trouble replicating the vast number of foods from Earth.
 * The Foundry: Forge of the Green Lantern rings and the Green Lantern battery. It is underground about two miles from the Central Power Battery and is guarded by an alien creature.
 * Hall of Great Service: Housing the massive Book of Oa - the Corps' lawbook and bible - the Hall of Great Service is a library of the stories and deeds of the finest Green Lanterns of all time. Like his father before him, Tomar-Tu recently took the position of archivist superior, filing every tale as it comes in.
 * Hazard Simulation Facility: All rookie Green Lanterns endure a series of tests to determine their viability in the field. The hazard simulation facility allows for safe, non-lethal training scenarios to be enacted.
 * Meeting Hall: Lanterns receive their briefings and assignments in the central meeting hall.
 * Memorial Hall: A memorial erected to Green Lanterns who lost their lives in the line of duty. A Green Lantern named Morro and his pet dratures are its cryptkeepers.
 * Guy's Place: A new restaurant owned by Guy Gardner, serving Earth's American fast foods, dinners, and both non-alcoholic and alcoholic beverages.
 * The Sciencells: The sciencells were constructed to contain the most ruthless criminals in the universe. They currently hold such prisoners as Lyssa Drak, Evil Star, Igneous Man, Grayven, and Alexander Nero. Superboy-Prime was the only inmate who wasn't imprisoned in a sciencell. The Guardians and the Green Lantern Corps sent him to a quantum containment field surrounded by a red Sun-Eater and guarded by fifty Green Lanterns. The Green Lantern Voz acts as warden of the sciencells. No inmate has ever been rehabilitated successfully.
 * Sector Houses: These safe houses allow Lanterns to hold criminals as they await escort back to the Oan sciencells. Limited recreational facilities are available to accommodate Green Lanterns in their travels.

Book of Oa
After Thomas Kalmaku used Jordan's ring to rebuild Oa, Kyle Rayner used his power as Ion to resurrect the Guardians. The book of Oa is now restored.

The Forbidden Chapter of the Book tells the prophecy of the Blackest Night, the final destruction of the Green Lantern Corps at the hands of their greatest enemies as it was told to Abin Sur by the demons of Ysmault.

Upon recruitment, a Green Lantern is expected to uphold certain principles of his/her/its duty. These principles include:
 * 1) The protection of life and liberty within the assigned sector.
 * 2) Following the orders of the Guardians without question.
 * 3) Noninterference with a planet's culture, political structure, or its population's collective will.
 * 4) Acting within local laws and obeying the local authority within reason (presumably, the Guardians' orders can overrule this when necessary).
 * 5) Taking no action against anyone or anything until they are proven to be a threat against life and liberty.
 * 6) Avoiding the use of equipment, resources or authority of the Corps for personal gain.
 * 7) Showing respect for and cooperating with other members of the Corps and the Guardians.
 * 8) Showing respect for life which includes restraint of force unless there is no reasonable alternative.
 * 9) Giving top priority to the greatest danger in the assigned sector.
 * 10) Upholding the honor of the Corps.

The book of Oa has been designated off-limits after being rewritten by the Guardians of the Universe to include ten new laws. Only the first four have been revealed:
 * 1) Lethal force is authorized against the Sinestro Corps.
 * 2) Lethal force is authorized against all enemies of the Green Lantern Corps.
 * 3) Physical relationships and love between Green Lanterns is forbidden within the Corps. This law is later repealed and relationships between Green Lanterns are allowed following the Blackest Night event.
 * 4) The Vega System is no longer outside of Green Lantern Corps' jurisdiction.

When the new laws are written, the book is revealed to be written in Interlac, which is the galactic universal language used by the 30th and 31st Century United Planets and Legion of Super-Heroes.

To enforce these principles, the Guardians closely monitor the activities of the Lanterns. If they feel a violation of Corps regulations occurred, they will summon the offender to Oa and hold a trial in which the charges are read and the Lantern is allowed to explain his/her/its actions. If the Guardians are not satisfied by the explanation, they have a number of disciplinary options which include:
 * Probation
 * Personal supervision by the Guardians on Oa
 * Temporary exile from the Lantern's homeworld
 * Ritual Trial of Endurance (a Lantern must attempt a dangerous passage through the Anti-Matter Universe)
 * Expulsion from the Corps
 * Prime Duty (when Superboy-Prime was an Oan prisoner, guard duty was used for punishment)