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Binary system

The compact object and blue supergiant star form a binary system in which they orbit around their center of mass every 5.599829 days. From the perspective of Earth, the compact object never goes behind the other star; in other words, the system does not eclipse. However, the inclination of the orbital plane to the line of sight from Earth remains uncertain, with predictions ranging from 27° to 65°. A 2007 study estimated the inclination as 48.0 ± 6.8°, which would mean that the semi-major axis is about 0.2 AU, or 20% of the distance from Earth to the Sun. The orbital eccentricity is thought to be only 0.018 ± 0.002, meaning a nearly circular orbit. Earth's distance to this system is calculated by trigonometric parallax as 1,860 ± 120 parsecs (6,070 ± 390 light-years), and by radio astrometry as 2,220 ± 170 parsecs (7,240 ± 550 ly).

The HDE 226868/Cygnus X-1 system shares a common motion through space with an association of massive stars named Cygnus OB3, which is located at roughly 2000 parsecs from the Sun. This implies that HDE 226868, Cygnus X-1 and this OB association may have formed at the same time and location. If so, then the age of the system is about 5 ± 1.5 million years. The motion of HDE 226868 with respect to Cygnus OB3 is 9 ± 3 km/s, a typical value for random motion within a stellar association. HDE 226868 is about 60 parsecs from the center of the association and could have reached that separation in about 7 ± 2 million years —which roughly agrees with estimated age of the association.

With a galactic latitude of 4° and galactic longitude 71°, this system lies inward along the same Orion Spur, in which the Sun is located within the Milky Way, near where the spur approaches the Sagittarius Arm. Cygnus X-1 has been described as belonging to the Sagittarius Arm, though the structure of the Milky Way is not well established.