The longest constellation in the night sky is HYDRA, which is made up of five letters. It is a large constellation located in the southern sky and is the largest of the 88 modern constellations. It is visible from most of the northern hemisphere during the summer months. It is also the sixth-largest constellation in the night sky, covering an area of 1, 303 square degrees. It contains two stars with known planets and has many deep-sky objects within its borders.