The Cimmerian Planet was the gathering place of the leaders of the United Alliance of Evil. It is a planet with orangish features resembling tectonic plates; nearby was an object resembling the Earth's moon.
It is first mentioned when a flaming headed man told Divatox to go to the Cimmerian Planet, which she did when she heard that the orders came from Dark Specter, Grand Monarch of Evil. At the beginning of Power Rangers In Space, the United Alliance of Evil, along with a disguised Andros, gathered on the Cimmerian Planet to celebrate Zordon's capture. Dark Specter appeared and told of his plans to conquer the universe before they discovered Andros among them.
The Cimmerian Planet was the beginning of all plots in Power Rangers in Space, telling of the universal domination conquest, how Zordon was captured at the hands of Dark Specter, and how Astronema would become the overall antagonist to the Space Rangers.
The Cimmerian Planet was presumably owned by the Alliance, maybe even the central world of the UAE. What happened to the planet afterwards is unknown after the Alliance's failed invasion of the universe an near-annihilation of all its forces.