61 CYGNI

first star whose distance from Earth (about 11 light-years) was measured (by Friedrich Wilhelm Bessel in 1838). The star is a visual binary the components of which revolve around each other in a period of about 650 years. They are of fifth and sixth magnitudes. Regular variations in the motion of the brighter component may indicate the presence of an invisible companion with about 1 percent the mass of the Sun, or 10 times that of the planet Jupiter.