There are 88 constellations in the night sky although not all of them will be visible from the northern hemisphere. Originally a constellation was a depiction of an object or an animal or a character of mythology made by joining certain stars in the night sky together with imaginary lines. But in the early 20th century the I.A.U. (International Astronomical Union) created boundaries within which the constellations reside. So now, technically a constellation is actually an area of sky rather than a group of stars.
Many of the constellations we know today were created by the ancient Greeks showing heroes and characters of Greek mythology but there are also many 'modern' constellations too depicting scientific instruments and navigational aids. Most of these are in the southern hemisphere.
Constellations exist only as works of the mind as the stars which make up constellations are in no way connected to each other. Think of constellations merely as a way of finding your way around the sky.
