A light-year was a unit of measurement used to measure interstellar distance. It was quantified as the distance that light travelled in a vacuum over the course of an Earth year. Time could be further measured in light-centuries. (TV: The Ribos Operation)
Known distances
From Earth
- Arcturus was 40 light-years from Earth. (PROSE: Only a Matter of Time)
- Vega 3 was 27 light-years from Earth. (PROSE: K9 and the Beasts of Vega)
- Aldebaran II was 65 light-years from Earth. (AUDIO: The Paradise of Death)
- Halcyon was 90 light-years from Earth. (AUDIO: The Resurrection of Mars)
- Sunday was 100 light-years from Earth. (PROSE: Wetworld)
- Beta Caprisis was 100 light-years from Earth. (PROSE: Sanctuary)
- Bellatrix was 324 light years away from Earth. (PROSE: Nightshade)
- Gger was 500 light-years from Earth. (PROSE: Listen - The Stars)
- Crimson Heart was 10,000 light-years from Earth. (TV: Death of the Doctor)
- The Orpheus constellation was 10,000 light-years from Earth. (TV: Aeolian)
- Gallifrey was 30,000 light years from Earth. (PROSE: The Devil Goblins from Neptune)
- Vandos was 60,000 light-years from Earth. (COMIC: Mr Nobody)
- Gorgos was 100,000,000 light-years from Earth. (TV: Eye of the Gorgon)
- Surobos was 420,000 light-years from Earth. (COMIC: Shipwreck!)
From other locations
- The Ao constellation and Qqaba were 9.6 light-years from Gallifrey. (PROSE: Lungbarrow)
- Ribos was 300 light-years from the Magellanic Clouds. (TV: The Ribos Operation)
- The Second Doctor once dematerialised the TARDIS 4 quadrillion light-years from the nearest galaxy. (PROSE: When Starlight Grows Cold)
- The Twelfth Cyber Legion was 20,000 light-years from Demon's Run. (TV: A Good Man Goes to War)
- Safeplace was about 32,000 light-years from Mars. (AUDIO: The Judgement of Isskar)
Known measurements
- The Mutter's Spiral galaxy was around 100,000 light-years in diameter. (PROSE: The Eyeless)
- The Morestran empire spanned 80,000,000 light-years. (PROSE: Zeta Major)
