Serpens (the snake) is one of the 88 modern constellations, and was also one of the 48 listed by Ptolemy. Among the modern constellations it is unique in sometimes being split into two pieces, Serpens Caput (representing the head of the snake) to the west and Serpens Cauda (representing the tail) to the east. Between these two pieces lies the constellation of Ophiuchus, the serpent holder.

Notable features

Since Serpens is regarded as being one constellation despite being split into two halves, the ordering of Bayer designations goes in order of brightness among both constellations.

Only one of the stars in Serpens is brighter than third magnitude, so the constellation is not easy to perceive. α Serpentis, named Unukalhai, is in the head part. δ Serpentis, also in the head, is a double star only 27 light-years from Earth. θ Serpentis, in the tail, is also double.

Stars in the head include α, β, γ, δ, ε, ι, κ, λ, μ, π, ρ, σ, τ, χ and ω Serpentis. Stars in the tail include ζ, η, θ, ν, ξ, and ο Serpentis.

Notable deep-sky objects

M5, a globular cluster approximately 8° southwest of α Serpentis in the head, is among the most beautiful in the sky.

M16 is a young open cluster associated with the Eagle Nebula, a diffuse nebula which is a region of current star formation in the tail.

Part of the Milky Way passes through the tail, as illustrated by the shaded regions of the star map.

Mythology

Serpens is the snake being grasped by Ophiuchus, the Snake-Handler. Originally they were considered a single Snake-Holder constellation, out of which developed an associated myth of the founding of medicine. It has no mythology prior to the 17th century associated with it seperately from Ophiuchus.