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T'Khut, or The Watcher, was the third planet in the Vulcan system, and shared a tidally locked co-orbit with Vulcan around a common center of gravity orbiting the star 40 Eridani A[3] - Vulcan and T'Khut were only 149,895.3579 kilometers apart. T'Khut was a Class G, Class H or Class K planet[2], and had one moon, T'Rukhemai (the "Eye of the Watcher"). (TOS novel: Sarek; ST references: Star Charts, The Worlds of the Federation; Last Unicorn RPG module: The Way of Kolinahr: The Vulcans)

The Watcher was known by a variety of names depending on when it was in the Vulcan year[1]; these included, T'Rukh, T'Kuht, T'Khul and Valdena. (TOS novel: Sarek; TOS novelization: Star Trek; Last Unicorn RPG module: The Way of Kolinahr: The Vulcans)

Humans named the world Charis, after a figure in Human mythology, who was married to Vulcan; complementing the Humans' name for the Vulcan homeworld. (TOS novel: Spock's World)


Because Vulcan and T'Khut were tidally locked the planet was only visible from one side of Vulcan, including filling the sky above Vulcan's Forge. The planet went through a full set of phases every day and filled thirty degrees of the sky when at full phase, reflecting forty times as much light as Earth's moon Luna. (TOS novel: Sarek)

The interaction between the worlds also resulted in huge tidal forces on both planets leading to persistent volcanic activity. T'Khut's volcanic eruptions and geysers could be witnessed from Vulcan, as could the dust storms that swept across the planet[4]. This hot inhospitable environment made the world almost entirely lifeless. (ST - New Worlds, New Civilizations short story: "Tempered by the Forge"; ST reference: The Worlds of the Federation)


In the 22nd century Ambassador Soval enjoyed watching Earth's moon Luna in the skies above San Francisco as it reminded him of T'Rukh. (ENT novel: Beneath the Raptor's Wing)

In 2381, the Zirkiv evacuated 269 people from T'Khut to Cor Caroli IX. (ST novel: A Singular Destiny)

In the Kelvin timeline, following the destruction of Vulcan in 2258 the USS Enterprise beamed aboard many Vulcans who had been working on bases on T'Khul. (TOS novelization: Star Trek)



Sirius sector block
Orion sector Kinjer system (Kinjer Prime) • Lackey system (Lackey III) • Reytan system (Reytan) • Starbase 24 (Starbase 24's system) • Una system (Una II) Beta Quadrant locator logo.
Orion trinary system Stars: Pi-3 Orionis trinary star (Orion A, Orion B, Orion C)
Planets and moons: I. Orion I • III.: Orion III/Orion Prime (Luna Orionis) • HoanThaspa
Risa sector Bomari system (Bomari II) • Donia system (Donia) • Gamma Orionis transwarp conduitImaga system (ImagaImaga II) • Koolhaas system (Koolhaas) • Omar system (Omar) • Tazi system (Tazi)
Risa system Stars and outposts: Epsilon Ceti AEpsilon Ceti B (Granicus binary) • Epsilon Ceti CEpsilon Ceti Outpost Alpha Quadrant locator logo.
Planets: Epsilon Ceti B I (Suam) • B II.: Risa (Inobe) • LowoionRusanej
Vulcan sector Beytan system (Beytan V) • Bhea system (Bhea) • Delta Volanis ClusterKei system (Kei III) • P'Jem system (P'Jem) • Pellme system (Pellme II) • Pico system (Pico) • Wolf 359 system
Vulcan system Stars: 40 Eridani A40 Eridani B40 Eridani C
Planets and moons: I. Ket-Cheleb • II & III.: VulcanT'Khut (T'Rukhemai) • IV. Tel-Alep • V. Kal-Apton • VI. Kir AlepVulcanis VIIDelta Vega


  1. 1.0 1.1 The TOS novel: Sarek established The Watcher as having different names at different times of the year, but only then refers to it as either The Watcher or T'Rukh. Other names and spellings have been given for the planet by different sources, which complement the idea of the world having a variety of names.
  2. 2.0 2.1 Three different sources provide contradictory information on what class of planet T'Khut is: The Worlds of the Federation's Class H is geologically active with a silicate crust and variable atmosphere (comparable to Gothos); Star Charts's Class G is described as geocrystalline, with a surface still forming and mostly carbon dioxide atmosphere (such as Delta Vega); and The Way of Kolinahr: The Vulcans identified the world as Class K, which is defined by another book in the series, Star Trek: The Next Generation Core Game Book, as a world with Earth-like gravity but with atmosphere that prevented Human habitation.
  3. T'Khut’s shared orbit with Vulcan is common to most references; however, at least one source contradicts this. The TOS novel: The Vulcan Academy Murders describes the planet as having an eccentric orbit which brought it close enough to Vulcan approximately once in each seven years where it appeared in the sky. After fourteen years, it approached Vulcan as closely as it ever did in a period of once every three centuries. At such times, the disk filled half the sky and when T'Khut was in the night sky it was as bright as day.
  4. The ST - New Worlds, New Civilizations short story: "Tempered by the Forge" describe T'Khut as airless, however the story also describes the planet's volcanic activity, which other sources such as The Worlds of the Federation and Sarek describe clouded sky and dust storms, indicating the planet does in fact have a rather turbulent atmosphere, and both of the possible planetary classifications from either The Worlds of the Federation and Star Charts give the planet some sort of atmosphere.
  • Spock's World, The Worlds of the Federation and Star Charts describe T'Khut as the smaller world of the Vulcan-T'Khut pairing. However, Sarek describes T'Khut as being twice as large as Vulcan.
  • Vulcan being visible in sky on the planet Delta Vega in the film Star Trek has led to speculation by some fans that Delta Vega might be an alternate designation for T'Khut. However the novelization of the film also references the Vulcan system's third planet, by the name T'Khul, which would seem to contradict this idea. Delta Vega being T'Khut is also inconsistent with T'Khut's common depiction as a hot volcanic world.

Appearances and References