T Aurigae

Lore & Background

Thomas David Anderson, an amateur astronomer in Edinburgh, reported being 'almost certain' he saw T Aurigae at 02:00 UT on 24 January 1892, when it was slightly brighter than χ Aurigae (apparent magnitude 4.74). He initially mistook it for 26 Aurigae, noting it seemed brighter than remembered. After seeing it twice more during the following week, he realized his mistake on 31 January 1892 and wrote to Ralph Copeland, the Astronomer Royal of Scotland. Copeland telegraphed William Huggins, who made the first spectroscopic observations on 2 February 1892, when the star was magnitude 4.5. Pre-discovery photographic plates allowed a light curve beginning in late 1891 to be constructed. In 1958, observations with the Crossley telescope revealed T Aurigae is an eclipsing binary with a period of 4.9 hours and an eclipse depth of 0.18 magnitudes. This discovery led to increased speculation that the nova phenomenon is connected to close binary star pairs; today it is believed all novae are binary stars with a donor star orbiting a white dwarf.

Reader's Guide

T Aurigae holds a significant place in astronomical history as the first nova ever observed spectroscopically, marking a turning point in the study of these explosive events. Its discovery by an amateur astronomer underscores the role of careful observation in advancing science. The later finding that T Aurigae is a short-period eclipsing binary was pivotal: it was only the third nova known to be such a system, and this discovery fueled growing speculation that novae arise from close binary interactions. Today, the binary model is fundamental to understanding novae, with matter transferred from a donor star to a white dwarf. The surrounding emission nebula, shaped like a peanut or prolate ellipsoid with a central waist, has been imaged from 1956 through 2019, showing expansion at about 0.01 arc seconds per year (≈350 km/s). This shell, resembling a planetary nebula, provides ongoing clues about the nova's outburst and evolution.

Did You Know?

• T Aurigae was the first nova to be observed spectroscopically, by William Huggins on 2 February 1892.
• Its discoverer, Thomas David Anderson, initially mistook it for 26 Aurigae before realizing his error.
• The nova's surrounding shell is roughly elliptical (25 by 19 arc seconds) and shaped somewhat like a peanut.
• In 1958, T Aurigae became the third nova discovered to be a short-period eclipsing binary, with a 4.9-hour period.

A Palimpsest of Heroes: Mythological Identities

The constellation Auriga carries an extraordinary palimpsest of mythological identities layered across cultures and centuries. In Greek tradition it is most commonly identified with Erichthonius, the chthonic son of Hephaestus raised by Athena, who invented the four-horse chariot and defeated the usurper Amphictyon to claim the Athenian throne. Zeus elevated him into the heavens in recognition of his ingenuity. Yet other Greek sources cast the figure as Myrtilus, Hermes's son and charioteer for Oenomaus, who met his death at the hands of Pelops after helping him win Hippodamia's hand. Still another identification links Auriga to Hippolytus, Theseus's son, whose chariot was wrecked after he rejected his stepmother Phaedra's advances. In late antiquity the poets Claudian and Nonnus saw Phaethon, the sun's son who lost control of his father's chariot and was struck down by Zeus's thunderbolt. Even Medea's dismembered brother, flung into the sea during the Argonauts' homeward voyage, found a place among Auriga's stars. The goat-herd association from earlier traditions wove through all these narratives, binding the charioteer to the pastoral.

Stellar Systems and Deep-Sky Treasures

Auriga hosts several of the most scientifically compelling stellar systems in the northern sky. Capella, the constellation's brightest star, is an unusual multiple star system and ranks among the most luminous points visible to the naked eye. Beta Aurigae presents itself as a fascinating variable, while Epsilon Aurigae has drawn intense study as a nearby eclipsing binary with an unusually long orbital period. The constellation's proximity to the winter Milky Way endows it with a rich population of bright open clusters; M36, M37, and M38 are particularly popular targets for amateur astronomers. A single prominent nebula, the Flaming Star Nebula, is associated with the variable star AE Aurigae. Auriga also serves as the radiant point for several meteor showers, including the Aurigids, Zeta Aurigids, and Delta Aurigids, as well as the hypothesized Iota Aurigids. With an area of 657 square degrees—half the size of Hydra, the largest of the 88 modern constellations—Auriga offers a vast canvas of celestial objects for observers in the northern hemisphere during winter evenings.

From Mesopotamian Crook to Ptolemaic Catalogue

The stars we now call Auriga have been catalogued and reinterpreted across millennia and civilizations. The earliest known record comes from Mesopotamia, where they appeared as a constellation called GAM, representing a scimitar or crook, alternatively named Gamlum or MUL.GAM in the MUL.APIN. This figure stood for a goat-herd or shepherd and incorporated most of the modern constellation's bright stars, though Elnath was traditionally shared with Taurus. Bedouin astronomers later organized the same stars into a herd of goats, each star representing one animal—a pastoral image that persisted into Greek astronomical tradition. In Chinese mythology, Auriga's stars were folded into several native constellations, including the celestial emperors' chariots, composed of the brightest stars. Ptolemy included Auriga among his 48 constellations in the 2nd century, and it has since remained one of the 88 modern constellations. Due to its northern declination, the full figure is visible only as far south as −34 degrees latitude, beyond which it sinks partially or entirely below the horizon.

The Charioteer, the Goat, and the Kids

Artistic representations of Auriga have long centered on a charioteer figure, though the details have shifted across centuries. The traditional image shows the driver holding a goat over his left shoulder, with two kids tucked under his left arm, while his right hand grips the reins of the chariot. Yet these reins have also been rendered as a whip in some illustrations, and depictions have been notably inconsistent over the years. The goat and kids form a distinct asterism with Capella, Epsilon Aurigae, Zeta Aurigae, and Eta Aurigae; the latter two were first named the Kids by the ancient Greek astronomer Cleostratus. Capella itself was sometimes treated as an independent constellation—called Capra, Caper, or Hircus, all relating to its goat-star status—by writers such as Pliny the Elder and Manilius. It was Ptolemy who merged the Charioteer and the Goats into a single constellation in his 2nd-century Almagest. Capella's mythological link to the she-goat Amalthea, who nursed the infant Zeus, further deepens the pastoral symbolism woven into the constellation's visual identity.