Auriga

The Charioteer of winter

Auriga, the Charioteer, is a large pentagon of stars high in the winter sky, lying in the Milky Way between Perseus and Gemini. It is easy to recognize thanks to Capella, a golden-yellow star at its north-western corner.

Capella lies far enough north that it is circumpolar from about 44°N, meaning it never sets. From somewhat farther south, such as Istanbul or New York, it dips below the northern horizon only for a few hours. On winter evenings it shines almost overhead.

How to find it

On January evenings, look straight up from mid-northern latitudes: the brightest star near the zenith is Capella. Another route starts at Orion. Go north from the Belt, past the Hunter's head between Betelgeuse and Bellatrix, and after about 30 degrees you reach Elnath, the southern corner of Auriga's pentagon; Capella lies about 18 degrees farther north.

The pentagon is about 15 degrees across. Going east from Capella and around, its corners are Menkalinan, Theta Aurigae, Elnath and Hassaleh. Elnath was once shared with Taurus, marking the tip of the Bull's horn; since the modern boundaries were set in 1930 it belongs to Taurus only.

Just south-west of Capella, three faint stars form a narrow triangle known as the Kids, the young goats of the Charioteer.

The main stars and their names

Capella (Alpha Aurigae) shines at magnitude about 0.08 and lies about 43 light-years away. Its name is Latin for 'little she-goat'. It is a system of two yellow giants, each a few times wider than the Sun, that orbit each other at less than the Earth–Sun distance. Their orbit is seen nearly face-on, so they never eclipse each other. A separate pair of faint red dwarfs, far from the giants, also belongs to the system.

Menkalinan (Beta Aurigae), magnitude about 1.9 and about 81 light-years away, has a name from the Arabic for 'shoulder of the rein-holder'. It is itself an eclipsing pair whose small dips are hard to notice by eye.

Hassaleh (Iota Aurigae), magnitude about 2.7, is an orange giant roughly 490 light-years away at the pentagon's south-western corner.

The Kids and a long eclipse

Epsilon Aurigae, the star at the tip of the Kids, is one of the strangest stars known. Every 27 years it fades by about three-quarters of a magnitude and stays dim for nearly two years. Something large and dark, now thought to be a huge disk of dust around a hidden companion star, passes in front of it.

The last eclipse ran from 2009 to 2011 and was followed by amateur and professional observers around the world. The next one is expected around 2036–2038. Zeta Aurigae, another of the Kids, is also an eclipsing binary, with a cycle of about 2.7 years.

Deep-sky objects for binoculars and small telescopes

Inside the pentagon, in the Milky Way, three open clusters sit in an almost straight line: M38, M36 and M37 from north-west to south-east. Each lies roughly 4,000 light-years away. Binoculars show all three as small hazy patches.

In a small telescope, M37 is the richest, with many faint stars packed around a brighter orange one. M36 is smaller and brighter, with a few bright stars, while M38 has a looser, cross-like shape. Comparing them at the same magnification is a good exercise in seeing.

Near the star AE Aurigae is the Flaming Star Nebula (IC 405), a cloud of gas and dust lit by a hot, fast-moving star. It shows well in photographs but is faint to the eye. Auriga also lies close to the galactic anticenter, the direction exactly opposite the center of our galaxy.

Mythology

The goat comes first. In Mesopotamia these stars were already linked with a goat, and later Greek writers identified Capella with Amalthea, the goat that nursed the infant Zeus. One of her horns became the horn of plenty.

The Charioteer is usually Erichthonius, a legendary king of Athens said to have invented the four-horse chariot, or Myrtilus, the charioteer of King Oenomaus. Old star maps show him holding the reins with a goat on his shoulder and two kids in his arm. In Turkish the constellation is called Arabacı, the Charioteer.

Practical observing tips

Auriga is best from December to March, between about 8 p.m. and midnight. Capella is bright enough for any city, and it twinkles in many colors when it is low in the north-east on autumn evenings.

For the clusters, use binoculars first to find the line of three, then switch to a small telescope at low power. To follow Epsilon Aurigae in the coming decades, note its brightness now against nearby Zeta and Eta Aurigae, so you know what 'normal' looks like.