Dyson sphere

A Dyson Sphere was a hollow sphere, with a sun at the centre, designed to completely enclose the star and collect all the energy that would otherwise escape into space. (PROSE: Lucifer Rising) The People lived in the inner shell of such a construct, known as the Worldsphere. (PROSE: The Also People, Walking to Babylon)

Romana II and K9 also had an adventure in a Dyson Sphere. (AUDIO: The Search)

Prior to her travels with the Seventh Doctor, Bernice Summerfield was part of a team of archaeologists who excavated the remnants of a Dyson Sphere around a white dwarf in the Vartaq Veil. Tidal stresses had pulled it out of shape until it degenerated into disconnected fragments, slowly leaking the atmosphere. The builders became nomadic and migrated from fragment to fragment. (PROSE: Lucifer Rising)

Behind the scenes

 * The Dyson Sphere takes its name from the Earth physicist who first proposed it,.
 * Most fictional depictions of a Dyson Sphere, including those in Doctor Who, are, in fact, a Dyson Shell, something generally considered to be an engineering impossibility. An actual Dyson Sphere is a swarm of energy-collecting satellites around a star; the "sphere" is the shape of that swarm or bubble, not a solid object.