A Stargate address is a coordinate system used by a Stargate to determine the position of a target gate in the Stargate Network. They are composed of a series of glyphs, at least seven depending on the intended destination, which when entered in the correct order allow the Stargate to establish a wormhole with another gate at the destination.
A Stargate address consists of two distinct parts: the destination and the starting location. The first six chevrons mark a three-dimensional area of space as the target. The last chevron is the point of origin, identifying where the Stargate is dialing from. Seven chevrons are used to dial within a galaxy, while the eighth and ninth are required for greater distances. The point of origin is always the last chevron, apart from the nine-chevron address, while any between it and the first six are modifiers that change how the system interprets the coordinates given. Assuming the dialing gate has enough power and neither is obstructed in any way, the wormhole will then form, allowing passage.
Because of stellar drift, most addresses are invalid by themselves. Dial Home Devices contain automatic update transceivers which allow the network to correct for stellar drift. This correlative update system causes the DHDs to occasionally dial other gates and update their position in the network. The Stargate on Earth lacks a DHD, so Stargate Command developed their own equation to compensate for stellar drift. A supercomputer using this equation was able to turn out two or three every month. While under the influence of the Ancient Repository of knowledge, Colonel Jack O'Neill developed a much more efficient equation for calculating stellar drift. (SG1: "Children of the Gods", "The Fifth Race", "Avenger 2.0")
Types of addresses
A seven-chevron address is the standard address used to connect to other gates within a galaxy. The first six chevrons mark the destination and the seventh chevron is the point of origin. (SG1: "The Fifth Race") Compared to eight- and nine-chevron addresses, the energy requirements to dial a seven-chevron address are minimal; the Dial Home Device present with most Stargates contain a power source sufficient to dial such addresses nearly indefinitely. The oldest known DHD, found in Antarctica, was still capable of dialing fifty million years (an estimate) after it was created, though its cold fusion reactor core was depleted shortly after it was recovered. (SG1: "Frozen")
Eight-chevron addresses are used to dial extragalactic gates, usually millions of light years away. (SGU: "Air, Part 1") In this address, an additional chevron is added between the destination and the point of origin, which serves as a distance calculation. Dialing another galaxy requires more energy than a Dial Home Device provides. For example, the single-use Power booster device (which provided 10x more power than normal) permitted dialing Othala in the Ida galaxy from Earth in the Milky Way galaxy. (SG1: "The Fifth Race") When dialing Atlantis in the Pegasus galaxy from Earth in the Milky Way galaxy and vice versa, a single Zero Point Module sufficed. (SGA: "Rising", "The Siege, Part 2")
In the Pegasus galaxy, the Atlantis' DHD was the only one known to be able to establish an eight-chevron lock because it possessed a unique, though removable control crystal. However, a sufficient power source is still required. (SGA: "Rising", "Home")
A nine-chevron address connects to the 1st generation Stargate on-board Destiny as well as back to Earth from Destiny. These two nine-chevron addresses are the only ones known to exist and have been dialed. A nine-chevron address always corresponds to a specific gates, regardless of its location or position. This is necessary for dialing Destiny, because being a ship, it is often in motion (only making brief stops). Thus, a nine-chevron address always remains the same and connects to the same gate regardless of the destination gate's position, including the point of origin. For example, the address to dial Destiny's gate always includes Earth's point of origin, even if dialing from a different planet. The Ancients likely selected Earth's point-of-origin because they launched Destiny from Earth. (SGU: "Air, Part 1", "Darkness")
Depending on the distance between the dialing and receiving gate, the energy requirements may be enormous. Destiny is several billion light years from Earth, which means that dialing Destiny requires large amounts of energy. Given that the Tau'ri do not posses the ability to create Zero Point Modules and must conserve existing ZPMs due to their rarity, this makes dialing Destiny difficult. As well, it is unclear how many ZPMs would be required to dial Destiny as well as how many times a connection could be established between Destiny and Earth before depleting the ZPMs. Destiny was only successfully dialed twice from the Milky Way: Icarus Base on P4X-351 and the Icarus-like planet. Both planets exploded due to their unstable Naquadria cores (which provide vast amounts of energy capable of dialing Destiny), although battles took place on both planets, involving energy weapons, possibly destabilizing the cores of each planet. (SGU: "Air, Part 1", "Darkness", "Incursion, Part 1", "Twin Destinies")
Although unconfirmed, it is possible that all Pegasus DHDs initially contained the unique control crystal permitting extragalactic dialing, but the Ancients removed them from all the DHDs when the Wraith threat emerged as a means of preventing them from attacking other galaxies. It is not known whether Milky Way DHDs possess the special control crystal.
There are three popular, unconfirmed theories regarding the mechanics of nine-chevron addresses (numbered):
- It is possible that all gates have a unique nine-chevron address, although this is not confirmed.
- The glyphs on Destiny-style Stargates represent some form of Ancient numeral system, and that the address is based on the direction and distance of the destination gate relative to the dialing gate.
- Nine-chevron addresses can and are used in Stargates that are located in or around 'top-secret' or 'need to know' Ancient facilities. Since nine-chevron addresses are not based upon a location in space, the destination can not be located via triangulation, using the six points in a normal seven or eight-chevron address, thus making use of this method of dialing a secure way. This theory also addresses why neither the SGC or Atlantis expedition have found Ancient facilities (other than the hangar in the Taranis outpost) for ship construction or manufacturing as knowledge about these worlds and how to access them would be strictly controlled by those who have a higher standing in their civilization, such as the Lantean Council, and not common knowledge amongst others.