Corona Borealis

Corona Borealis's brightest star, Alphecca, is already described elsewhere as the crown's one named jewel. A much fainter, far stranger star in the same small arc has drawn more attention from professional astronomers in recent years than Alphecca ever has.

T Coronae Borealis, nicknamed the Blaze Star, is a recurrent nova, a binary system that periodically brightens by a factor of thousands within a single night before fading back to invisibility to the naked eye. Recorded outbursts occurred in 1866 and again in 1946, roughly eighty years apart, and the pattern of dimming that preceded the 1946 eruption was observed recurring in the star in the early 2020s, leading astronomers to watch closely for another outburst on a similar timescale.

A recurrent nova of this kind is understood to result from a white dwarf pulling material from a companion star until enough has accumulated on its surface to trigger a sudden burst of nuclear fusion, a process that repeats roughly on schedule rather than happening once, unlike an ordinary nova or a supernova that destroys or permanently alters the star involved.

Ariadne's crown, set among the stars for a wedding gift in Greek myth, holds within its faint arc a star whose most notable property has nothing to do with jewels or marriages: it is one of the very few stars in the sky whose next dramatic event astronomers can actually predict in advance.

Corona Borealis, the Northern Crown, is a small but elegant northern constellation, one of Ptolemy's forty-eight, whose seven chief stars form a graceful arc like a jewelled diadem or crown. In Greek myth it is the crown of Ariadne, given her by Dionysus and set among the stars, its brightest jewel the star Alphecca, whose name means the broken one, from the Arabic for the broken ring of stars. The semicircle is easy to recognise between Bootes and Hercules. In astronomical tradition the constellation is a pattern of stars rather than a zodiac sign. These are the features of Corona Borealis as the classical and modern traditions describe it, distinct from any astrological reading; its clear ring of stars has made it one of the more beloved of the small constellations of the northern sky.

Corona Borealis is one of the few small Ptolemaic constellations with no seventeenth or eighteenth-century additions carved from its immediate borders, its compact arc of stars evidently too tightly bound as a recognisable shape for later astronomers to see any use in subdividing the faint space around it. Alphecca's own broken-ring etymology, discussed at length under its own entry among this atlas's stars, gives the crown's brightest jewel a name that describes the shape of the whole constellation rather than any property of the star itself.