Sigma Draconis (σ Dra, σ Draconis) is a 4.7 magnitude star located at a distance of 18.8 light-years in the constellation Draco. Its traditional name is Alsafi.
The star is a main sequence dwarf of spectral type G9. Formerly it was classified as K0, with the spectrum of this star serving as one of the stable anchor points by which other stars are classified. The radius has been directly measured using interferometery with the CHARA Array, which yields a result of 77.8% of the Sun's radius. It has 87% of the Sun's mass, but the luminosity of this star is only 43% that of the Sun. The projected rotation rate (v sin i) is relatively low at 1.5 km/s. It is considered a slightly metal-poor star, meaning that it has a lower proportion of isotopes with masses more than helium when compared to the Sun.
The temperature, luminosity and surface activity appear to vary slightly in a manner very similar to the sunspot cycle, although the full length of the cycle has not yet been determined.8 The total variability is among the lowest of all stars that have been measured by the Hipparcos spacecraft.
The components of Sigma Draconis's space velocity are U=+36, V=+40 and W=-10 km/s. This gives the star an unusually large orbital eccentricity about the Milky Way galaxy of 0.30 (compared to 0.06 for the Sun.) The mean galactocentric distance for the orbit is 10.3 kiloparsecs (about 34,000 light-years).
As of 2007, no Jupiter-size or larger companion had been detected about the star and there was no indication of excess infrared radiation that would be evidence of circumstellar matter (such as a debris disk).
Sigma Draconis in Space Opera:
- "Spock's Brain?" (1966), episode of Star Trek: The Original Series? written by Gene L. Coon? as by Lee Cronin and directed by Marc Daniels?, as part of the film, television, and print franchise originated by Gene Roddenberry?. The Sigma Draconis system contains three inhabited planets: Sigma Draconis III, IV and VI. Sigma Draconis III? is home to a medieval civilization, while the inhabitants of Sigma Draconis IV? have reached a post-industrial level. The crew of the Enterprise does battle on Sigma Draconis VI?, an ice-blasted world populated by primitive Morgs? (who before their fall were more scientifically advanced than the Federation), in a campaign to
- Starforce: Alpha Centauri ?(1974), board game designed by Redmond Simonsen and published by Simulation Publications. Humanity is reaching out into local interstellar space, and making first contact (and war) with a number of alien species. In the Sigma Draconis system, 18.8 light-years distant, they encounter the L'Chal Dah?, an advanced spacefaring race.
- Dune II: The Building of a Dynasty? (1992), computer game developed by Westwood Studios (Brett Sperry et al.) and published by Virgin Interactive. The game revolves around an interstellar struggle between the Houses of Atreides, Harkonnen, and Ordos. House Ordos does not appear in any of the Dune novels, but it does in several Dune computer games. The Ordos are mercenary; they care for nothing, save power and wealth. Their home planet, featured in the Ordos House emblem, is Sigma Draconis IV (Ishkal).
- Honor Harrington? (1993–), series of novels by David Weber?. Located in the Sigma Draconis system, Beowulf is the oldest human colony, having been founded almost two thousand years before the events in the Honor Harrington saga. Beowulf?, an important member of the Solarian League?, derives a measure of prosperity from the proximity of a wormhole junction that makes the planet a major trading partner of the Star Kingdom of Manticore?. Recent developments have tempted Beowulf to secede from the Solarian League.
- Known Space. In Ringworld RPG the system was attacked by Kzin in 2449