Battlestar Galactica (RDM)
Earth is the alleged location of the Thirteenth Colony, destination of the Thirteenth Tribe of Kobol, as attested in the Sacred Scrolls. Earth is first mentioned by Commander Adama during a speech made after funeral services in the wake of the devastating Cylon attack on the Twelve Colonies, claiming that it is a real place and that top military leadership knew its location (see Mini-series). In a private conversation with new President Laura Roslin immediately afterward, Adama admits that he has not the slightest idea where Earth may be, if it exists. His true motivation was inspirational; he intended to bolster the morale of the population (especially his beleaguered crew) in the aftermath of the near-annihilation of humanity.
While she is initially skeptical, going so far as to rebuke Adama for his dishonesty, Roslin's faith grows perceptibly throughout the events of the first season. This transition is at least partly due to her use of the hallucinogen Chamalla as an alternative treatment to her terminal breast cancer. These hallucinations are increasingly interpreted as prophetic vision by Roslin, and they continue as the Fleet ultimately finds the legendary Kobol in Kobol's Last Gleaming, Part I. Eventually, a religious artifact is recovered which reveals clues of the location of Earth (Home, Part II).
In a mysterious chamber, the stars of the Twelve Colonies are represented in the twelve Zodiacal constellations, as viewed from Earth, recognized by Roslin as the shapes of the original flags of the Twelve Colonies. The chamber itself was intended by its builders to be a stylized replica of the night sky of the Earth, from which all twelve Colonies could be seen. This is corroborated by Starbuck, who quotes scripture, saying that Earth was the place where the people of the Thirteenth Tribe could look up into the sky and see their twelve brothers. Captain Apollo also recognized the Lagoon Nebula, also represented in the night sky of the mystery chamber. Apparently this astronomical object is known to Fleet personnel, since Commander Adama remarked that this celestial body would take some time to reach.
Battlestar Galactica (TOS)
Earth is the Thirteenth Colony; its settlers having departed long ago from Kobol after the same environmental cataclysm which caused the Exodus of the Twelve Tribes and made Kobol uninhabitable. As stated in the Book of the Word, the Thirteenth Tribe left opposite the other Twelve Tribes, the information of their destination residing in the tomb of the Ninth Lord of Kobol. (Lost Planet of the Gods)
Transmissions from Earth -- i.e. the Apollo Moon Landing -- were picked up by Captain Apollo in the Celestial Temple on an obsolete Gamma frequency, though the copy of the transmission was destroyed in the attack on the Cylon basestar. (The Hand of God)
Technology from Earth appears to be present at Athena's station in Saga of a Star World. As she runs a diagnostic on Starbuck's Viper the words MADE IN USA appear on the screen. This appears to indicate the diagnostic program may have been left over from a time when Colonials had contact with Earth. An alternate explanation is that USA could coincidently be a region on one of the colonies.
Notes (Non-Canonical)
- In Galactica 1980, Earth was discovered, but, much to the dismay of Adama and the survivors, the humans on Earth were underdeveloped and would not be able to defend themselves from the Cylons.
- In one of the extras included on the five-disc DVD release of the first season of Battlestar Galactica, Edward James Olmos (the actor portraying Commander Adama) remarks in a very jocular fashion that they will never reach Earth. Mary McDonnell (the actress who plays Laura Roslin) covers his mouth and tries to hush him while laughing. Although loyal fans may question the trustworthiness of this statement, it is known that the creators keep a "Bible" to the show, to which the actors presumably have access.