what is serpens?
A constellation of the northern hemisphere.
Serpens
Serpens ("the Serpent", Greek ) is a constellation of the northern hemisphere. 
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Serpens [SEP] Introduction
Serpens ("the Serpent", Greek ) is a constellation of the northern hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations defined by the International Astronomical Union. It is unique among the modern constellations in being split into two non-contiguous parts, Serpens Caput (Serpent Head) to the west and Serpens Cauda (Serpent Tail) to the east. Between these two halves lies the constellation of Ophiuchus, the "Serpent-Bearer". In figurative representations, the body of the serpent is represented as passing behind Ophiuchus between Mu Serpentis in "Serpens Caput" and Nu Serpentis in "Serpens Cauda".