Antares

Antares is Alpha Scorpii, and it is the clearest case in the sky of an astrological attribution embedded in the star's own name.

The Greek Antares is generally understood as anti-Ares, rival of Ares, Mars, because the star resembles the planet in both colour and brightness and can be mistaken for it near the ecliptic. The name is therefore a record of the observation, not a later interpretation of it. Ptolemy duly assigns it the nature of Mars, with a Jupiter component, and the Mars half was never in doubt.

The astronomy supports the observation exactly. Antares is a red supergiant, spectral type M1.5 Iab, apparent magnitude around 0.96 and variable, at roughly 550 light years. It is one of the largest stars known by diameter, estimates place its radius at several hundred times the Sun's, large enough that if placed at the centre of the solar system its surface would lie beyond the orbit of Mars. Its surface temperature is low, around 3,500 K, which is why it is red; its enormous luminosity comes from area rather than temperature.

It has a hot blue companion, Antares B, of spectral type B2.5 V, which is difficult to see against the primary's glare and appears greenish by contrast when glimpsed.

Antares is a star near the end of its life. It will exhaust its fuel and explode as a supernova, on a timescale of order a million years, imminent astronomically and irrelevant on any human scale.

It sits close to the ecliptic, about four degrees south, so Mars passes near it every couple of years. That recurring conjunction is the observation the name records: an observer can watch planet and star stand together, closely matched in colour and brightness, and see directly why the Greeks named one for the other.

The traditional reading of Antares (courage, ferocity, headstrong daring, honours won and lost through rashness, a sudden fall), is one of the more coherent fixed-star delineations, and it is worth tracing.

Ptolemy supplies the raw material: a Mars nature with a Jupiter admixture. That pairing is what generates the standard reading. Mars alone would give simple violence; Jupiter alone would give expansion and honour. Together they give something more specific, great ambition that destroys itself, magnitude of enterprise combined with a lack of restraint. The tradition's reading of Antares is a fairly disciplined inference from Ptolemy's two words, which is more than can be said for many.

The elaborated delineations (the specific predictions of ruin, of danger from fire and from beasts, of self-inflicted disaster), are from the later compilers, and in English from Robson in 1923, drawing on Arabic and Renaissance material.

Antares is one of Agrippa's Behenian fifteen, paired with sardonyx and with birthwort. It is also counted among the four Royal Stars, as the Watcher of the West, a scheme discussed under Aldebaran, and one that should be treated as unsourced.

There is a genuine older layer. Antares is the heart of the Scorpion in the Babylonian tradition as well as the Greek, and Babylonian astronomical texts treat the Scorpion constellation as significant. Rochberg's work on Mesopotamian celestial divination sets out what that material actually says, which is considerably more concerned with omens for kings and states than with individual character. The shift from state omens to personal delineation is one of the largest changes in the history of the subject and it happens in the Hellenistic period.