Vesta

Vesta was discovered on 29 March 1807 by Heinrich Olbers, the fourth asteroid found, and it is the brightest of them, occasionally just visible to the unaided eye. It is the second most massive body in the belt and is differentiated, with a crust, mantle and iron core, which makes it more like a small planet than a rubble pile; the Dawn spacecraft orbited it in 2011 and 2012 and imaged the enormous Rheasilvia impact basin at its south pole. A family of meteorites found on Earth, the howardite-eucrite-diogenite group, has been traced to Vesta. The name is that of the Roman goddess of the hearth, the Greek Hestia, whose sacred fire in the temple at Rome was tended by the Vestal Virgins, priestesses bound to thirty years of chastity and service. Modern astrology, from the 1970s asteroid literature onward, reads Vesta for dedication, focused service, sacred work and the withholding of the self from ordinary claims.

The Roman cult behind the name was civic rather than domestic, which sharpens the modern reading. The fire in the temple of Vesta was the hearth of the state, not of a household, and letting it go out was a public emergency requiring expiation. The six Vestals who tended it were freed from paternal authority, could make wills and give evidence, and held a legal standing no other Roman woman had, in exchange for thirty years of service and chastity enforced by burial alive for a breach. The figure the asteroid is named for is therefore not a symbol of domestic retreat but of a woman's withdrawal from private claims into public office, which is closer to the modern astrological reading than the hearth image suggests.

Vesta orbits at about 2.36 astronomical units with a period near 3.63 years, the shortest of the four large asteroids, so it moves through a sign in about three and a half months on average. Its eccentricity is modest at about 0.09 and its inclination is only about 7 degrees, which keeps it inside the traditional zodiacal band for the whole of its orbit.

That last figure sets it apart from the other asteroids in this atlas. Where Pallas at nearly 35 degrees of inclination is never actually among the stars of the sign it is reported in, and Juno at 13 degrees leaves the band for part of each circuit, Vesta stays where the ancients drew the zodiac. Of the modern asteroid points it is the one whose longitude corresponds to something a person could go outside and look at.

They could look at it with the naked eye, too, at a favourable opposition. Vesta reaches about magnitude 5.1 at its brightest, which makes it the only asteroid ever visible without optical aid, and it would have been visible in antiquity to anyone who knew where to look and had no reason to distinguish it from a faint star.

It is also the best studied. Roughly 525 kilometres across and the second most massive body in the belt after Ceres, it was orbited by the Dawn spacecraft through 2011 and 2012, which mapped a differentiated body with a basaltic crust and an enormous impact basin at its south pole.

Vesta was the fourth asteroid discovered, found by Heinrich Wilhelm Olbers in 1807, the same astronomer who had found Pallas five years earlier. Its glyph is a stylised hearth or altar fire, originally credited to the German mathematician Carl Friedrich Gauss, who had already made his name computing Ceres's recovered orbit and went on to design a symbol showing the altar of Vesta's cult with its sacred flame. That fuller image circulated in nineteenth-century astronomical tables before falling from use.

When Eleanor Bach compiled her 1973 "Ephemerides of the Asteroids," the source generally credited with returning Ceres, Pallas, Juno and Vesta to astrological practice, she introduced a simplified rendering of Gauss's hearth glyph, and it is this pared-down form, rather than the original altar image, that became the standard Vesta symbol in the astrological software and printed ephemerides used today. Vesta's brightness, the very quality that had let earlier observers glimpse it without a telescope, meant its glyph history was documented unusually well from the start, with Gauss's original altar image reproduced in the astronomical almanacs of the period well before any of the four asteroids had astrological significance at all.