Unukalhai is Alpha Serpentis, apparent magnitude about 2.6, at roughly 74 light years. It is an orange giant, spectral type K2, an evolved star swollen off the main sequence. It lies in the western half of Serpens, the only constellation split into two separate pieces, the serpent's head and tail, by the figure of Ophiuchus the serpent-bearer between them. The Arabic name, from unq al-hayya, means the neck of the serpent, its position on the coils.
Serpens is unique among the modern eighty-eight constellations in being formally divided into two disconnected pieces, Serpens Caput to the west and Serpens Cauda to the east, split by the intervening figure of Ophiuchus; Unukalhai, marking the neck, sits in Caput near the boundary, close to where the ancient figure's head met the body before the later division formalised the split into official, separately bounded regions. Unukalhai's position near the boundary between Serpens Caput and the intervening figure of Ophiuchus places it close to one of the more visually confusing junctions in the whole northern sky, three constellations meeting in a comparatively small area. Its evolved, reddened appearance to the eye sets Unukalhai visibly apart from the whiter, hotter stars that dominate much of the rest of this catalogue.
Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Almagest (Mathematike Syntaxis)Claudius Ptolemy