Nocturne is a planet in the Circinus Sector of the Perseus Quadrant. It is an Earthlike planet with a temperate climate, known for its exceptionally long nights.

450,000,000 humans live on Nocturne, spread more or less evenly across the planet's three continents. Noctumus is the planetary capital. It is a member of the New Commonwealth of the Galaxy, and participates in the political and cultural lige of the New Commonwealth. It engages in trade and diplomacy with other New Commonwealth worlds and with planets in the Free Worlds Alliance. Its citizens serve in the New Commonwealth Space Fleet.

Augustus and Marcus Lear died in a shuttle accident on Nocturne while flying from Nova (in orbit) to the wedding of the daughter of the Chief Diplomat. The crash was blamed on Android Agents from Ecco 1, seeking to keep Nocturne from joining the New Commonwealth.