Serpens

Serpens is a constellation in the northern celestial hemisphere, split into Serpens Caput and Serpens Cauda by Ophiuchus. It is the only constellation divided into two separate regions by another constellation.

Serpens Caput: The western portion of Serpens, depicting the serpent’s head. This half lies west of Ophiuchus and contains the constellation’s brightest star.
Ptolemy: A Greek-Egyptian astronomer and mathematician whose works shaped ancient astronomy. Ptolemy included Serpens among the 48 constellations in the Almagest.
Messier 16: An open star cluster embedded in the Eagle Nebula in Serpens Cauda. It is a prominent deep-sky target within the constellation’s tail.
Hercules: A large northern constellation representing the mythological hero Heracles. Hercules borders Serpens Caput to the north.
Gemini: A zodiac constellation in the northern sky, represented by the twins Castor and Pollux. Unlike Serpens, Gemini forms one continuous constellation region.
Serpens Cauda: The eastern portion of Serpens, depicting the serpent’s tail. This half lies east of Ophiuchus and completes the constellation’s divided form.
Almagest: A second-century astronomical treatise by Ptolemy that catalogued stars and constellations. Its star catalogue preserves an early systematic description of Serpens.
Eagle Nebula: An emission nebula and star-forming region catalogued as IC 4703, surrounding Messier 16. The nebula’s famous pillars lie in Serpens Cauda.
Aquila: An equatorial constellation representing an eagle, containing the bright star Altair. Aquila borders Serpens Cauda to the south and east.
Circumpolar star: A star that never sets below the horizon for a given observer’s latitude. Serpens is not circumpolar for most inhabited northern latitudes, unlike stars near the north celestial pole.

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