A star was a ball of gas composed of hydrogen and helium. Stars existed throughout the universe and often were orbited by planets. Perihelion was when a planet got closest to its star. (HOMEVID: The Zero Imperative)
In the pre-universe, stars were doughnut-shaped. (PROSE: Millennial Rites) When the universe was rationalised they became spherical. (TV: The End of the World, 42, Amy's Choice, The Rings of Akhaten)[additional sources needed] In the after-universe, the stars were spherical, but usually green. (COMIC: The Stockbridge Child)
In general, only more advanced species were capable of manipulating or using stars.
The Time Lords were capable of controlling stars to their own ends. They used stellar manipulators like the Hand of Omega to control stars. (TV: Remembrance of the Daleks) The Tenth Doctor said they invented black holes. (TV: The Satan Pit) They used the black holes to power their time travel. (TV: The Three Doctors, The Deadly Assassin)
The Great Old Ones could be returned to their bodies by the positions of the stars. Unfortunately for them, the constant expansion of the universe meant the stars would never return to their proper positions. (PROSE: White Darkness)
Other references Edit
The reality bomb caused the destruction of all reality, making the stars seem to "go out". (TV: Turn Left, Journey's End) The total event collapse, the destruction of the universe, caused every star to supernova. (TV: The Pandorica Opens) The stars went out when the Great Intelligence invaded the Doctor's time stream to turn all of his victories into defeats; this was witnessed by Madame Vastra on Trenzalore. (TV: The Name of the Doctor)
130 years after rendering Jack Harkness a mortal by cutting him off from the Time Vortex, John Hart realised that something was wrong as stars appeared closer than they should have. Jack revealed to John that, since he was a fixed point in time, John had endangered the universe by allowing him to die, the moving stars being a result of time and space contracting. Ultimately, the alternate timeline John had created was negated when Jack perished. (AUDIO: The Death of Captain Jack)