AU at periapsis and 124 AU at apoapsis. The leisurely orbit of the pair has made it difficult to pin down their respective masses, and the accuracy of these values remain somewhat controversial. In the future this issue may be resolved through the use of asteroseismology. 61 Cygni A has about 11% more mass than 61 Cygni B. The system has an activity cycle that is much more pronounced than the solar sunspot cycle. This is a complex activity cycle that varies with a period of about 7.5±1.7 years. The starspot activity combined with rotation and chromospheric activity is a characteristic of a BY Draconis variable. Because of differential rotation, this star's surface rotation period varies by latitude from 27 to 45 days, with an average period of 35 days. The outflow of the stellar wind from component A produces a bubble within the local interstellar cloud. Along the direction of the star's motion within the Milky Way, this extends out to a distance of 30 AU, or roughly the orbital distance of Neptune from the Sun. This is lower than the separation between the two components of 61 Cygni, and so the two most likely do not share a common atmosphere. The compactness of the astrosphere is likely due to the low mass outflow and the relatively high velocity through the local interstellar medium. 61 Cygni B displays a more chaotic pattern of variability than A, with significant short-term flares. There is an 11.7-year periodicity to the overall activity cycle of B. Both stars exhibit stellar flare activity, but the chromosphere of B is 25% more active than for 61 Cygni A. As a result of differential rotation, the period of rotation varies by latitude from 32 to 47 days, with an average period of 38 days. There is some disagreement over the evolutionary age of this system. Kinematic data gives an age estimate of about 10 Gyr. Gyrochronology, or the age determination of a star based on its rotation and color, results in an average age of . The ages based on chromospheric activity for A and B are 2.36 Gyr and 3.75 Gyr, respectively. Finally the age estimates using the isochrone method, which involve fitting the stars to evolutionary models, yield upper limits of 0.44 Gyr and 0.68 Gyr. However, a 2008 evolutionary model using the CESAM2k code from the Côte d'Azur Observatory gives an age estimate