Unukalhai

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

The tradition gives Unukalhai the nature of Saturn with Mars, one of the more malefic pairings, and Robson reads it for misfortune, accidents, chronic disease and, in the lurid manner of the older sources, danger by poison, the serpent supplying the theme. This is a delineation to treat with the standard caution: the combination of the two malefics is a schematic assignment, and the catalogue of specific disasters is late compilation, not observation. The star's dependable identity is as the bright orange giant marking the neck of the one constellation that a second figure cuts in half.

The specific pairing of chronic disease with a Saturn-Mars star follows the standard medical-astrological logic of the older tradition: Saturn was read for what is prolonged, wasting or cold in its nature, Mars for what is acute, inflamed or violent, and a star combining both was accordingly read as prone to illnesses that begin suddenly and then settle into something lasting, a piece of internally consistent theory rather than an arbitrary label. No source earlier than the compiling tradition assigns Unukalhai its specific chronic-disease delineation, and as with several of the Saturn-Mars stars in this catalogue, the reading should be read as a schematic nineteenth or twentieth century addition.