Cygnus is a constellation in the northern sky. Cygnus means "swan" in Greek. There is a pattern of stars in Cygnus that is called the Northern Cross. This is because the pattern of stars looks like a cross. The constellation Crux (constellation) has a pattern of stars that is called the Southern Cross. The astronomer Ptolemy listed Cygnus in the 2nd century when he made a list of constellations.