47 Cygni
47 Cygni is a triple star system in the northern constellation of Cygnus, and is located around 4,000 light years from the Earth. It is visible to the naked eye with a combined apparent visual magnitude of 4.61. The system is moving closer to the Earth with a heliocentric radial velocity of −4.6 km/s. The dual nature of this system was recognized by Annie Cannon in 1912, and she assigned the pair separate Henry Draper Catalogue identifiers. They orbit each other with a period of around . The primary component is itself a spectroscopic binary in a near  circular orbit with a period of around . The "a" sin "i" value for the primary is , where "a" is the semimajor axis and "i" is the orbital inclination. It has been repeatedly resolved by speckle interferometery since 1973. Radio emission was detected from this system in 1985/86. The supergiant primary is a slow irregular variable with an amplitude of about 0.1 magnitudes. Its close companion has 57% of the mass of the Sun. The secondary is a hot B-type main-sequence star, but still 2.5 magnitudes fainter than the primary.