Auriga: The Charioteer

Auriga is a pentagon of stars riding high on cold winter evenings, and its brightest point is doing something you would never guess by looking at it. Capella looks like a single steady point of gold light. It is actually two yellow giant stars, locked in a close orbit, blurred together into one point by distance alone.

A chariot inventor who carries a goat

Auriga is most often identified with Erichthonius of Athens, a mythic figure credited with inventing the four-horse chariot — a genuinely useful bit of technology to get credit for. But the charioteer in the sky is not shown driving anything. Instead he carries a she-goat, Amalthea, marked by Capella itself, along with her kids nearby. It is an odd pairing of stories glued onto one figure, chariot inventor and goat-herder both, and the sky doesn't bother to resolve the tension.

Chinese astronomers looked at the same patch of sky and saw something entirely different: they grouped Capella with the stars around it as Wuche, the Five Chariots, and tied the pattern to the harvest of the five staple grains. Two civilizations, looking at the same bright point, reaching for chariots in both cases but for very different reasons — one a hero's invention, the other an agricultural calendar.

Just how bright is Capella, really

Capella sits at magnitude 0.08, which makes it the sixth-brightest star in the entire night sky, not just in its own small pentagon. That is a genuinely rare thing for a "minor" constellation to host — most of the sky's brightest stars belong to constellations people already know by name, and Auriga is not usually one of them. Menkalinan, Beta Aurigae, is a white eclipsing binary at magnitude 1.9, and Mahasim, Theta Aurigae, is a blue-white star at magnitude 2.62, rounding out the pentagon's brighter points.

Three star clusters in one small patch

Auriga carries three good open clusters, all within reach of binoculars from a reasonably dark site. M37 is the richest of the three, dense with faint stars packed close enough together to reward a slow sweep rather than a quick glance. M36 is brighter and more compact, an easier first target if you're new to hunting clusters. M38 has a distinctive cross-like shape when you actually resolve its stars rather than seeing it as a single blur. Having three separate clusters this close together in one constellation is unusual — most patterns get one, if any, and Auriga's pentagon happens to sit over a genuinely rich stretch of the winter Milky Way.

Working the three in order — M36, then M38, then M37 — is a reasonable route if you're starting out with a low-power eyepiece or a decent pair of binoculars, since they sit roughly in a line and each one is a slightly different flavor of the same basic object: a loose cluster of stars born together and still drifting as a group.

Finding Auriga in your own sky

Auriga is a northern-hemisphere constellation with a best month of February, when it sits high overhead on winter evenings, well clear of the horizon murk that swallows fainter stars lower down. Capella itself is bright enough to find even from a city, which makes it a good first landmark before you go hunting the clusters, and once you have it, the rough pentagon of the rest of the charioteer falls into place around it fairly naturally.

What this means for you tonight

Find Capella first — at magnitude 0.08 it will be one of the brightest points in your winter sky and hard to miss even with some light pollution. From there, the three clusters sit inside the pentagon shape Capella anchors, but you will need binoculars and a darker sky than city glow allows to actually resolve M36, M37, and M38 into stars rather than smudges; light pollution and the Bortle scale is worth reading before you decide how far out of town to drive. February evenings are Auriga's best window, so if you're checking your sky map on a summer night, don't be surprised to find the charioteer below your horizon entirely.

For the mechanics behind constellation boundaries, read what a constellation really is, and for why 0.08 puts Capella in such rare company, read how star brightness works.