Alphecca

Alphecca is Alpha Coronae Borealis, apparent magnitude about 2.2, at roughly 75 light years, the brightest star of the small, distinct semicircle of the Northern Crown. It is an eclipsing binary of the Algol type: a white main-sequence star with a fainter yellow companion that passes in front of it, dimming the pair slightly on a period of about seventeen days. Both stars are girdled by discs of dust. Its names capture its setting, Alphecca from a word for the break or gap in the ring of stars, and the Latin Gemma, the jewel, for its place as the gem of the crown.

The seventeen-day eclipse period is short enough that an observer patient enough to track Alphecca's brightness over a few weeks could detect the dimming with nothing more than careful naked-eye comparison to nearby stars, in principle the same method by which Algol's much larger dip was noticed centuries before spectroscopy explained either system. Alphecca's identification as the crown of Ariadne rather than any other mythological crown is the majority reading among classical sources, though a minority tradition connects the figure instead with a crown belonging to Dionysus himself rather than to his bride. Alphecca's dust discs, one around each stellar component, are a relatively rare configuration for a close binary of this kind to display simultaneously.

Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Almagest (Mathematike Syntaxis)Claudius Ptolemy

The tradition gives Alphecca the nature of Venus with Mercury, reading it for honour, artistic and poetic gifts, and dignity, a benefic delineation fitting a jewel, carried in English by Robson. Alphecca is one of Agrippa's fifteen Behenian stars, paired in the Renaissance talismanic scheme with topaz and with rosemary and trefoil, which again gives it, unusually, a documented early-modern stone-and-herb correspondence rather than a modern guess. The crown it heads has been read as Ariadne's, set in the sky after Dionysus, which suits the star's gentle and honourable reputation.

Alphecca's Agrippa correspondences are recorded specifically as the gemstone topaz and the herbs rosemary and trefoil, one of the more fully preserved of the fifteen entries; the scheme paired each Behenian star not only with a stone and plant but with a magical sigil meant to be engraved on the appropriate material while the star was rising, though the sigils themselves survive only as diagrams in the manuscripts and print editions of De Occulta Philosophia rather than as anything easily rendered in words. Agrippa's stone-and-herb correspondences were intended for practical talisman-making, engraving the star's sigil onto the named gem while the star was suitably placed and binding the plant to it, a magical technology largely abandoned in mainstream astrology by the eighteenth century even as the bare delineations survived.