61 Cygni

61 Cygni is a binary star system located in the constellation Cygnus, approximately 11.4 light-years from Earth. It consists of two K-type main-sequence dwarf stars, designated 61 Cygni A (HD 201091) and 61 Cygni B (HD 201092), which orbit each other with a period of about 659 years.

61 Cygni A is slightly larger and more luminous than 61 Cygni B. Both stars are less massive and cooler than the Sun, and appear orange in color.

Historically, 61 Cygni holds significance as one of the first stars (after Alpha Centauri) found to have a measurable parallax, which allowed for the determination of its distance. This landmark measurement, performed by Friedrich Bessel in 1838, was a crucial step in establishing the scale of the universe and demonstrated that stars were much further away than previously thought.

Due to their relative proximity and brightness, 61 Cygni A and B are popular targets for amateur astronomers. While no planets have been confirmed orbiting either star, their proximity makes them attractive candidates for future planet searches. The system's age is estimated to be relatively old, potentially billions of years, making planet formation possible.

The designation "61 Cygni" follows the Flamsteed designation system, a star catalog numbering system based on right ascension within each constellation.