KY Cygni is a red star in the Cygnus constellation. It is one of the largest stars known and with a radius about 1,420 R☉ (6.6 au). If it was placed at the center of the Solar System, it would extend past the orbit of Jupiter (or Saturn). It is also one of the most luminous stars, with about 300,000 or more times the Sun's luminosity. It is about 5,000 light-years away.