Ophiuchus constellation from Johann Bayer's star atlas Uranometria Omnium Asterismorum, 1603. Ophiuchus is a large constellation located around the celestial equator. Ophiuchus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations defined by the International Astronomical Union. It was formerly referred to as Serpentarius, a Latin word meaning the same as its current name. Ophiuchus is located between Aquila, Serpens and Hercules, northwest of the center of the Milky Way. The southern part lies between Scorpius to the west and Sagittarius to the east. In the northern hemisphere, it is best visible in summer. It is located opposite Orion in the sky. Ophiuchus is depicted as a man grasping a serpent; the interposition of his body divides the snake constellation Serpens into two parts, Serpens Caput and Serpens Cauda, which are nonetheless counted as one constellation. Johann Bayer's star atlas Uranometria Omnium Asterismorum was the first atlas to cover the entire celestial sphere. The Uranometria introduced a new system of star designation which has become known as the Bayer designation. His atlas added 12 new constellations to fill in the far south of the night sky, which was unknown to ancient Greece and Rome.