Eye of Harmony
The Eye of Harmony, also known as Rassilon's Star, was a power source for the Time Lords. It was created by suspending time around an exploding star in the act of becoming a black hole, harnessing the potential energy of a collapse that would never occur. According to the Eleventh Doctor, you "rip[ped] the star from its orbit, [and] suspend it in a permanent state of decay." (TV: Journey to the Centre of the TARDIS)
Legend
According to The Book of the Old Time, Rassilon, "with a great fleet" found the Eye of Harmony in a "black void" and returned it to Gallifrey at which "the people rejoiced". (TV: The Deadly Assassin)
- The passage, in full, implies that the Eye of Harmony may refer not to the black hole but the singularity contained within it.
Legends stated that the Eye of Harmony watched every Time Lord, wherever they went. (PROSE: The Adventuress of Henrietta Street)
In the Panopticon
In the time of the Fourth Doctor, the Eye of Harmony lay secretly under the floor in the centre of the Panopticon. The Time Lords had forgotten its location. Some believed it to be mythical or no longer in existence. (TV: The Deadly Assassin)
The Rod and the Sash of Rassilon
The ancient artefacts ceremonially given to the Lord Presidents had a practical function to do with the Eye. The Rod of Rassilon opened the floor of the Panopticon like a key, allowing a black hexagonal obelisk to rise from the floor. This contained the Eye of Harmony. The Sash of Rassilon, also given to the President, supposedly served as means of protecting the wearer against the forces of a black hole. The practical functions of the Rod and the Sash and the true nature of the Eye of Harmony remained unknown to most on Gallifrey. (TV: The Deadly Assassin)
Attempt to open the Eye
The Fourth Doctor deduced the true use of the artefacts by interpreting enigmatic passages in The Book of the Old Time. He also realised that the name, the Eye of Harmony, symbolically described a black hole contained and balanced against the mass of the planet Gallifrey by Rassilon's engineering. The Master had also separately come to the same conclusion. He deduced that the Sash of Rassilon would give him immunity to the forces unleashed by the Eye if opened (it didn't, due to being damaged by the time he used it). If it had opened, the Eye of Harmony would have functioned as a normal black hole and destroyed Gallifrey and also the Master, who had hoped it would trigger a new cycle of regenerations for him. (TV: The Deadly Assassin)
- Omega also used a black hole in order to enable the Gallifreyans to acquire the power of time travel.
Sontaran Invasion
When the Sontarans invaded Gallifrey, their leader, Stor, wished to destroy the Eye. They hid their attack by having the Vardans front it. After the Vardans were defeated by the Fourth Doctor, the Sontarans attacked. They were prevented from destroying the Eye when the Doctor defeated them. (TV: The Invasion of Time)
Dalek Invasion
When the Daleks unleashed the Apocalypse Element on the Seriphia Galaxy, the Sixth Doctor and Romana attempted to use the power of the Eye to contain it, but it was insufficent. The Daleks on Gallifrey added their own mental energy to the Eye, which did contain the Element and created a new galaxy for them to transform into their new empire. During this incident the Doctor reprogrammed Gallifrey's security systems so that the Eye could only be opened by a human retina pattern. (AUDIO: The Apocalypse Element)
Inside the Doctor's TARDIS
An aspect of the Eye of Harmony existed within the Doctor's TARDIS, at least during the later part of his seventh and eighth incarnation. The Eye of Harmony was said to be the TARDIS's primary power source.
The Eye responded to a physical linking device. The particular structure of a human eye had the effect of opening it. . Leaving the TARDIS's Eye open for too long would result in space-time distortion. (TV: Doctor Who)
If opened partially, the Eye gave visions of the past. (PROSE: The Eight Doctors)
All TARDISes built after a certain point, including the Type 40 the Doctor used, had a mathematically modelled duplicate of the Eye with all its attendant features. (PROSE: The Quantum Archangel)
While in Caliburn House, 1974, the Eleventh Doctor was able to utilise a "subset of the Eye of Harmony" to enter a pocket universe by running cables from the TARDIS. (TV: Hide)
The Eleventh Doctor, Tricky and Gregor van Baalen once came across the Eye of Harmony when trapped inside the TARDIS. At that point, the Eye had the appearance of a star. (TV: Journey to the Centre of the TARDIS)
Dalek Eye of Harmony
During their advancement, the Dalek Empire developed the use of harmonic energy derived from their own Eye of Harmony, based on that of the Time Lords. Several adjustments were made through the use of temporal barrier technology used on Kar-Charrat. (AUDIO: The Time of the Daleks)
Behind the scenes
No explanation of how the Eye of Harmony could exist in two places at once exists on-screen. A popular fan explanation states that each TARDIS had a link to the actual Eye of Harmony (possibly in the same way the Time Lords transmitted energy from Gallifrey to the TARDIS in TV: The Three Doctors). The BBC official guide to Doctor Who confirms this, and states that, following the destruction of Gallifrey, the Doctor's TARDIS now powers itself with the energy from time rifts. The Eight Doctors explains:
It wasn't the Eye of Harmony at all of course, not really. Just a symbolic manifestation, an aspect, of the Great Eye of Harmony on Gallifrey.
