Cygnus is a constellation in the northern hemisphere. It contains the 19th brightest star in the night sky, Deneb, which is also the 20th-brightest star overall. The constellation is named after a swan, and its shape is often likened to a cross or a coat hanger.

Cygnus contains approximately 150 stars that can be seen with the naked eye from Earth. The brightest stars in the constellation form the asterism known as the Northern Cross, which is a prominent feature of the summer night sky. The brightest stars in the Northern Cross are Deneb, Albireo, Gamma Cygni, Delta Cygni, and Epsilon Cygni.

In addition to the stars that can be seen with the naked eye, Cygnus also contains a number of stars that can only be seen with the aid of a telescope. Some of the most famous of these stars include Eta Cygni, which is a variable star that changes in brightness over time, and X-ray binary Cygnus X-1, which is a powerful source of X-rays and is thought to be a black hole.

Overall, Cygnus is a beautiful and fascinating constellation that is full of interesting stars. It is a popular target for stargazers of all levels, from beginners to experienced observers.