Which constellation is commonly known as the Swan?

The constellation commonly known as the Swan is Cygnus.

Cygnus is the northern constellation whose name comes from the Latinized Greek word for “swan.” It is one of the most recognizable patterns in the northern summer sky, where its stars trace a bird flying along the Milky Way.

Cygnus is also famous for the Northern Cross, an asterism formed by several of its bright stars. Deneb, its brightest star, marks the swan’s tail and forms one point of the Summer Triangle with Vega in Lyra and Altair in Aquila. Albireo is commonly pictured at the tip of the swan’s beak, although it is best known as a colorful double star in small telescopes.

The constellation was among the 48 listed by the Greek astronomer Ptolemy in the 2nd century and remains one of the 88 modern constellations recognized today. Greek and Roman myths connect it with several different swans, including stories involving Zeus, Orpheus and Cygnus of Liguria. Cygnus lies directly across the Milky Way, so it contains many star clusters, nebulae and other deep-sky objects.