Regulus (α Leo, α Leonis, Alpha Leonis) is the brightest star in the constellation Leo and one of the brightest stars in the night sky, lying approximately 77.5 light years from Earth.

Regulus is a multiple star system consisting of four stars. Regulus A is a binary star consisting of a blue-white main sequence star of spectral type B7V, which is orbited by a star of at least 0.3 solar masses, which is probably a white dwarf. The two stars take approximately 40 days to complete an orbit around their common centre of mass. Given the extremely distorted shape of the primary, the relative orbital motion may be notably altered with respect to the two-body purely Keplerian scenario because of non-negligible long-term orbital perturbations affecting, for example, its orbital period. In other words, the third Kepler law, which holds exactly only for two pointlike masses, would be no longer valid because of the highly distorted shape of the primary.

At a distance of around 4,200 AU from Regulus A is a binary star system that shares a common proper motion. Designated Regulus B and Regulus C, the Henry Draper Catalogue number for this pair is HD 87884. The first is a K2V star, while the companion is approximately M4V. The companion pair has an orbital period of 2,000 years and is separated by about 100 AU.

Regulus in Space Opera

  • BattleTech? (1984), wargame and related products launched by The FASA Corporation. Regulus is the capital system of the Duchy of Regulus?, one of the founding states of the Free Worlds League?.
  • Frontier: Elite II? (1993) and Frontier: First Encounters? (1995), computer games written by David Braben et al. In the games, Regulus has no permanent settlements, although minor mining operations do occur within the Regulus system.
  • Babylon 5? (1993–1998), television series developed and written by J. Michael Straczynski?. The Regulus system is the location of the Earth Alliance's? first extrasolar colony.
  • Descent: FreeSpace – The Great War? (1998), computer game developed by Volition, Inc. and published by Interplay Entertainment. Regulus is the greatest stronghold of the Neo-Terran Front? during their rebellion against the Galactic Terran Vasudan Alliance?.
  • "Kir'Shara?" (2004), episode of Star Trek: Enterprise? written by Mike Sussman?, as part of the film, television, and print franchise originated by Gene Roddenberry. Regulus is the staging area for a massive pre-emptive strike by the Vulcan High Command on Andoria?, based on specious intelligence suggesting that the Andorian Imperial Command is planning to adapt their vessels with a powerful Xindi weaponry.
  • In the Escape Velocity game by Ambrosia Software it is the system of New France and Regulus II.

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