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Serpens is a constellation. Its name is Latin for snake, and it is unique among the modern constellations in being split into two separate sections, Serpens Caput (the snake's head) to the west and Serpens Cauda (the tail) to the east. Between these two halves lies the constellation of Ophiuchus, the serpent holder. Serpens was one of the 48 constellations listed by the 2nd century astronomer Ptolemy and it remains one of the 88 modern constellations.


Notable features


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

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 210 light-years from Earth. θ Serpentis. also named Alya ("the snake" in Arabic), 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.

Deep-sky objects

Messier 5, a globular cluster located approximately 8° southwest of α Serpentis in the head.

Messier 16 is a young open cluster associated with the Eagle Nebula, a diffuse nebula which is a region of current star formation in the tail.

MWC 922, a nebula in the Mount Wilson Catalog, is a Symmetric Bipolar Nebula notable for its appearance as a perfectly symmetrical square or rectangle. It is also known as IRAS 18184-1302, and located at RA: 18:21:16 DEC: -13:01:27, near M16 in Serpens Cauda. The MWC is from Mount Wilson Observatory.

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