⚷ Chiron

Named for the Greek centaur Chiron

Healing Teaching Medicine Wisdom

Which sign is Chiron in now?

Achilles and the Centaur Chiron by Pompeo Batoni
Achilles and the Centaur Chiron Pompeo Batoni, 1746 Galleria degli Uffizi, Florence The centaur Chiron sits beside the young Achilles, who holds a lyre, under a tree by the sea. Public domain, via Wikimedia Commons

The wise centaur who raised heroes, taught healing, and gave up his immortality.

The centaur

Chiron was a centaur, part man and part horse, and Homer calls him “most righteous of the Centaurs.” He was the son of Kronos (Saturn) and Philyra, a daughter of Okeanos, and lived in an ancient rocky cave on Mount Pelion. Heroes were brought to him as boys: Pindar says “wise-hearted” Chiron raised Jason under his roof, Achilles was given to him to bring up, and he reared Asclepius and taught him medicine and hunting. Pliny the Elder credits him with discovering the science of herbs and drugs. In Apollodorus’s account, an arrow Heracles shot at other centaurs struck Chiron in the knee by accident. The wound would not heal, and he wished to die but could not, because he was immortal, until Prometheus offered himself to Zeus to be immortal in his stead. Ovid says Chiron was then given a body of “twice seven stars” in the sky.

How the minor planet got its name

Charles Kowal found Chiron on photographs taken with the 122-cm Schmidt telescope at Palomar Observatory in October 1977. In their 1979 report, Kowal, William Liller and Brian Marsden proposed the name Chiron and suggested it had once been an ordinary minor planet, pushed into its far-out orbit by collisions and close encounters with Jupiter and Saturn. In 1989 Karen Meech and Michael Belton saw a fuzzy glowing cloud around it, the coma that marks a comet, and Chiron was reclassified as a comet too; it is also listed as comet 95P/Chiron. Other icy bodies found later in orbits crossing the outer planets’ were given the class name Centaurs.

Symbols

Medicinal herbs Mount Pelion Fourteen stars

The minor planet

A small icy body among the giant planets. Its unstable, stretched orbit crosses Saturn’s and passes just inside Uranus’s, and one trip around the Sun takes about 50 years. It is thought to be made like a comet’s nucleus, a mixture of water ice, other frozen gases, organic material and silicate dust. So far from the Sun, the gases that escape to make its coma are probably more volatile ones than water, such as carbon monoxide and carbon dioxide. Short dips in starlight seen when Chiron passed in front of stars could be caused by a ring of material about 324 km from its center, astronomers have suggested.

Diameter
166 km 0.05 × the Moon’s
Spins once in
5.9 hours
Length of year
50.7 Earth years one trip around the Sun
Distance from the Sun
2,049 million km 13.7 AU (Earth = 1), on average

Figures from NASA JPL’s Small-Body Database, which names the study each one comes from; the mass is worked out from JPL’s figure for its gravity. Comparisons with the Moon and Earth use NASA’s Planetary Fact Sheet.

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