Cygnus, constellation in the northern sky at about 21 hours right ascension and 40° north in declination. The brightest star in Cygnus is Deneb, the 19th brightest star in the sky. Along with Vega and Altair, Deneb is one of the stars of the prominent asterism, the Summer Triangle. The Milky Way Galaxy runs through Cygnus. This constellation also contains such notable objects as Cygnus X-1, the first known black hole; the Cygnus Loop, a large supernova remnant; and the North American Nebula, a cloud of interstellar gas shaped much like that continent. The star 61 Cygni (11.4 light-years from Earth, the 15th nearest star) was the first to have its distance measured. In Greek mythology this constellation represented the form that the god Zeus took to seduce either the Spartan queen Leda or the nymph Nemesis.