NO Aurigae

Lore & Background

In 1969, Olin Jeuck Eggen announced that the star, then called HR 1939, is a variable star. It was given its variable star designation in 1972. NO Aurigae is listed in the General Catalogue of Variable Stars as a slow irregular variable, indicating that no regularity could be found in the brightness variations. Other studies have suggested possible periods of 102.1, 173, and 226 days, and would classify it as a semiregular variable star. The maximum visual magnitude range is 6.05–6.50.

Most studies of NO Aurigae treat it as a red supergiant member of the Auriga OB1 stellar association at about 1.4 kpc. On this basis it would have a luminosity around and a radius around. NO Aurigae is an MS star, intermediate between spectral type M and S. These are typically asymptotic giant branch stars which can appear with supergiant spectra due to their large size and low mass. Possible detection of technetium in the spectrum is a symptom of the third dredge-up which occurs only in late AGB stars.

Reader's Guide

NO Aurigae holds significance as an unusually luminous asymptotic giant branch star, offering a rare opportunity to study the late evolutionary stages of intermediate-mass stars. Its classification as a slow irregular variable, with some evidence for semiregular periods, highlights the challenges in characterizing the pulsations of evolved stars. The star's MS spectral type, intermediate between M and S, and the possible detection of technetium in its spectrum, point to the third dredge-up process that enriches the surface with s-process elements. As a member of the Auriga OB1 association, it provides a benchmark for understanding the properties of AGB stars in a known stellar environment. Its faint naked-eye visibility under good conditions makes it accessible to amateur astronomers interested in monitoring its brightness changes, while professional studies continue to refine its variability and evolutionary status.

Did You Know?

• NO Aurigae was originally designated HR 1939 before being given its variable star name in 1972.
• It is an MS star, intermediate between spectral types M and S.

The Charioteer's Many Faces

Auriga has never settled on a single identity. In the Greek tradition, the constellation most commonly represents Erichthonius, the half-divine son of Hephaestus raised by Athena, who is credited with inventing the four-horse chariot and using it to defeat the usurper Amphictyon and claim the Athenian throne. Zeus honored his ingenuity by placing his Sun-like chariot among the stars. Yet other tellings cast the figure as Myrtilus, Hermes's son and charioteer for Oenomaus, who was murdered by the victor Pelops after helping him win Hippodamia's hand; Hermes then elevated him to the sky. A third tradition 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 identified the constellation with Phaethon, Helios's son, who lost control of the solar chariot and was struck down by Zeus's thunderbolt before his father placed him in the heavens. Scholars suggest the Greeks may have created the constellation simply to celebrate the chariot's central role in their own society.

The Goat, the Kids, and Capella

Capella, Auriga's brightest star, carries a rich pastoral mythology. It is traditionally identified with Amalthea, the she-goat who nursed the infant Zeus on Crete. Together with Epsilon Aurigae and the two stars known as the Haedi—Zeta and Eta Aurigae, first called the Kids by the ancient Greek astronomer Cleostratus—Capella forms a small asterism of a mother goat with her young. An alternative myth ties Capella to a nymph who owned Amalthea; in that telling, Zeus skinned the Gorgon-faced goat and wore its hide as his aegis, an act that helped defeat the Titans. Historically, the goat-and-kids group was once treated as a separate constellation. Pliny the Elder and the poet Manilius referred to Capella under names like Capra, Caper, or Hircus, all emphasizing its goat-star character. It was Ptolemy who, in his 2nd-century Almagest, merged the Goats into the Charioteer, creating the unified Auriga we recognize today.

A Treasury of Deep-Sky Wonders

Auriga's position near the winter Milky Way makes it a magnet for observers. Beyond its notable stars—Capella, an unusual multiple system among the sky's brightest; Beta Aurigae, a fascinating variable; and Epsilon Aurigae, a nearby eclipsing binary with an unusually long period that has drawn intensive study—the constellation hosts three celebrated open clusters: M36, M37, and M38, all popular targets for amateur telescopes. The Flaming Star Nebula, linked to the variable star AE Aurigae, adds a striking emission object to the region. Auriga also serves as the radiant for several meteor showers, including the Aurigids, Zeta Aurigids, Delta Aurigids, and the hypothesized Iota Aurigids. The constellation is large, spanning 657 square degrees—roughly half the area of Hydra, the largest of all 88 modern constellations. Because of its northern declination, it is fully visible only down to latitude minus 34 degrees, beyond which it sinks partially or wholly below the horizon.

From Mesopotamian Scimitar to Chinese Chariots

The stars we now call Auriga have been woven into sky lore across many civilizations. The earliest recorded reference comes from Mesopotamia, where they appeared as a constellation named GAM, representing a scimitar or crook, alternatively called Gamlum or MUL.GAM in the MUL.APIN catalog. The crook symbolized a goat-herd or shepherd, and the figure encompassed most of the modern constellation's bright stars, excluding Elnath, which was shared with Taurus. Bedouin astronomers later reimagined the stars as a herd of goats, an association that flowed into Greek tradition before the charioteer identity took hold. In Chinese mythology, Auriga's stars were folded into several native constellations, including the celestial emperors' chariots, composed of the constellation's brightest stars. Ptolemy's 2nd-century list of 48 constellations cemented Auriga's place in the Western catalog, and it remains one of the 88 modern constellations recognized today.