The constellation of Charioteer (Auriga - Aur)

The constellation of Charioteer

Auriga is a boreal constellation, very well visible in our skies even in cities that are too bright. It is recognizable for the presence of Capella (magnitude 0) and for its position next to the twins Castor and Pollux ("Pollux and Castor" in order of brightness) and just above the Taurus with the two stellar ammasi of the Hyades and the Pleiades. The Auriga has several interesting objects: stars close to us (four below 50 light years), a dozen stars 50 times bigger than the Sun (with 2-3 monsters not bad!), some beautiful deep sky objects and finally it has several stars baptized with a name. But let's proceed in order, as usual.

Representation over time

Let us observe the representations of this coachman over time: Hevelius shows a young man with a kid (Capella, in fact) on his shoulder, a riding crop and a bridle in his hand and a hat that looks like a painter or sculptor on his head.

the Charioteer according to Hevelius

In the version of the Uranometria the young man seems a little more grown up

the Auriga according to the Uranometry

while Stellarium shows us with a much bigger goat held in his arms and no longer on his shoulder.

the Auriga according to Stellarium

The name, the history & the myth of Charioteer

Represented in Mesopotamia as a coachman, the Auriga appears depicted since the most ancient times with a goat on his back or in the act of cradling a goat, then identified in the goat Amaltea. Mythologically, in fact, Capella (the alpha star) is Amaltea, the little goat that was Zeus' nanny when he was a child and lived with the shepherd of Mount Ida. It was his mother, Gea, who took him to the mountain to take him away from his father Saturn who, for fear of being ousted by his children, used to eat them.
According to some it was Eritonius, son of Mother Earth and Hephaestus (Vulcan, for the Romans, the blacksmith of the gods), who became king of Athens and introduced the four-horse chariot, the quadriga.

In another myth, the Auriga represents the unhappy coachman Blueberry. King Oenomaus, famous for his passion for horses, did not want his beautiful daughter Hippodamia ("the horse tamer") to marry. So he called for a coachman's race in which every one of his daughter's suitors would race. The winner would have his hand, but every challenger defeated would lose his life. The horses of Oenomaus, faster even than the North Wind, gift of Ares (Mars) were unbeatable, so that the king was sure he could win and thus kill every suitor. When it was the turn of Pelope, son of Hermes, the gods decided to intervene. Poseidon (Neptune), ancient god of horses and ruler of the seas, gave Pelope a golden chariot drawn by winged steeds. In order to be sure of victory, Pelope, accomplice of Hippodamia, agreed with Myrtle, Oenomaus' coachman, to replace the chariots in the king's chariot hubs with wax copies. In exchange he promised the cunning coachman half of the kingdom and the privilege of the first wedding night with Hippodamia. At the climax of the race the wheels of Oenomaus' chariot slipped off and the king was mortally wounded and before he died he cast a curse against Myrtleberry. Pelope, Hippodamia and Myrtle celebrated the victory with a ride on the chariot in triumph. Stopping for refreshment, the lust for the reward caught Blueberry, but Hippodamia repelled him. Pelope then struck the coachman, took the reins and made to go with the chariot, turned, and as he left again he kicked Blueberry, which made him fall and die instantly. Hermes, who had the trick and cunning to his credit, honoured the coachman by taking him among the stars.

Deep sky objects

Let's now start an analysis of the various Deep Sky objects present in this large constellation, in the HST photos, starting from three open star clusters catalogued by Messier.
The first one is M36 which doesn't look very starry.

the open cluster M36

The cluster M37 instead appears more populous with many bluish stars and other more yellowish ones.

star cluster M37

while M38 is definitely more overcrowded with stars more or less the same color as M37

the star cluster M38

Another star cluster, definitely poorer, is the equally deserving NGC 1664

few stars... but it's still a star cluster (NGC 1664).

Now instead we see two very beautiful and richly colored nebulae: IC 410 which has areas of distinctly different colors

the colorful IC410 nebula.

and finally we can admire IC 405 the Flaming Star Nebula (nebula of the Flaming Star) called obviously so for the bright red color that distinguishes it, while the flaming star is the bright one in the middle of the picture.

the red Flaming Star Nebula

This star, known as AE Aur (HIP 24575) we see it shot in this other photo in another wavelength.

the Flaming Star (AE Aur) taken in another wavelength

Three fastest stars

The star AE Aur, a blue dwarf variable of spectral class O, placed at almost 1500 al, has a peculiar characteristic, together with two other stars (μ Col and 53 Ari, respectively of the Dove and the Aries): these three stars have in common a very high, anomalous motion, so much to have received the nickname of "runaway stars" (term ignobly and uselessly translated by some parts as "runaway stars"). As to why these stars are so fast, there are two hypotheses by scientists, both of which are particularly suggestive: the three stars were literally fired away following a collision of two groups of binary stars or due to a supernova explosion within a multiple star system.

The first hypothesis is based on the discovery that the three stars (and perhaps there is a fourth one yet to be discovered) are actually moving away from the same point, corresponding to the position of the star ι Ori , one of the four that make up the famous Trapeze of Orion, a group of stars completely immersed in the M42 nebula. A collision between two pairs of stars, which occurred two and a half million years ago, would therefore have catapulted these three "runaway stars" in three different directions, so much so that today we see them in three constellations completely different and quite distant from each other.

The other hypothesis of the explosion of a supernova, always near the star ι Ori, would instead be supported by the presence of the so-called Barnard's Loop, a nebula with a really huge emission, centered on the Orion nebula, which would be the residue of what is left of the explosion: in this case we hypothesize the presence of several "runaway stars" of which these three have been discovered so far. The Barnard Loop can be seen very well in this photo (a sort of orange semi-circle), in which we can recognize well known objects, no less than the entire constellation of Orion!

the Barnard's Ring in the constellation Orion.

In this absolutely fantastic photo, which was not by chance chosen as APOD in 2010, we recognize well known objects and stars: to simplify the identification, look at the next photo. The three stars aligned diagonally in the center are the Orion Belt, at the bottom left there is Betelgeuse, at the top right Rigel and almost at the center of the arch just M42 with more to the left the famous $nebulosa$ Horsehead. To the photo I added the names of the objects and other lines that should help to recognize the constellation and Barnard's Ring.

Orion and Barnard's Ring

Stars nearby

the double QY Aur system closely filmed

After this fantastic binge of cosmic wonders, we get a little closer to get to know QY Aur (Gliese 268A). It's a variable star of spectral class M4 just 20 to the Sun (which from over there appears almost of fourth magnitude): since the star is a double, I asked my friends Quiauri to capture their binary system with my trusty time machine camera-ship called Celestia. In this picture we can see what our Sun looks like from the QY Aur: right in the middle of a curious and nice arc of stars, really interesting...

the Sun seen by λ Aur

The other three nearby stars are the variable v538 Aur (IP26779), the star λ Aur (called Alhiba II) and the several times mentioned Capella (α Aur, whose name must be pronounced with the "e" well open, since it is Latin), respectively 40, 41 and 42 light years from us.

Seen from the proximity of the three stars, in all the three cases the Sun is already very weak, but at least in the photo taken with my friends Alibabani, the Sun appears immersed in the Milky Way!

Big stars

comparison between Auriga's stars and other notes

Definitely that of Auriga is a constellation very rich in cues and important objects: passing to the biggest stars here we meet half a dozen of them to be frightened, as we can see from the comparison diagram I made for Auriga. Can you see ψ1 Aur, a star monster of spectral class K5, with a diameter of 393 times our poor Sun? I drew it at the top right, half buried by other stars!

In this table I've listed the 10 biggest stars of the Auriga constellation: in the three columns we have respectively the diameter with respect to the sun, the name of the star (with the possible link to the photo of the same star seen from the considerable distance of 10 UA (that of Saturn from the Sun!) and finally the spectral class.

ψ1 Aur is really hallucinating and disturbing, from a distance not so small as the usual 10 Astronomical Units: from here this orange monster of class K5 illuminates and burns everything nearby, appearing with a diameter of almost 18° on the sky. As you can see, unlike many other monsters we have encountered in our analysis of the constellations, this supergiant, since it is class K, shines a strong yellow-orange light.

The second one is a little easier to find in the diagram: it is π Aur, up there on the upper left, with an imposing diameter of 237 times the Sun: seen from the canonical 10 UA it is no less threatening than the previous one.

With just (just to say!) 152 times our Sun, we finally see a supergiant star of class F0, ε Aur (Almaaz) shining with a dazzling white light and with a diameter of more than 7° in the sky of the poor Mazziani, who populate a rocky planet with a distinctly red color.

Slightly smaller (or rather less big) are the two stars ζ Aur (Haedus I) and ι Aur (Kabalinan) respectively with 138 and 121 times the size of our small Sun: the corresponding photos allow us to see two other yellowish-white monsters.

To appreciate even better the differences in colour between the various stars mentioned and photographed, I suggest you to click on the first photo and move to the next ones with the right arrow: in this way you will see their apparent size decrease and you will appreciate their different colour. Pressing the left arrow instead you will go back.

Other big stars are υ Aur (73x, class M), followed by a poker of class K stars, 66 Aur, 2 Aur, 6 Aur and 1 Aur, respectively, with 59, 54 and two 48 times that of our yellow dwarf. Not bad!

The names of the stars

Our coachman has several stars with a proper name, many of them grouped by family:

  • Capella (α Aur): Latin name, small goat
  • Menkalinan (β Aur): the shoulder of the bridle bearer
  • Elnath (γ Aur): shared with the constellation Taur (β Tau), of which it represents one of the horns
  • Praja (δ Aur): sir
  • Almaaz (ε Aur): the goat
  • Haedus I and II and η Aur): from the Latin, the little goats
  • Mahasim (θ Aur): the pulse
  • Kabalinan (ι Aur): the ankle of the one who supports the reins
  • Alhiba I, II and III, λ and σ Aur): the tent
  • Dolones from I to X (from ψ1 to ψ10 Aur): the scourges of the bridle (a kind of cat with nine tails!)

The visibility of the Auriga

The northernmost part of the constellation, and in particular Capella, begins to see itself low on the horizon almost to the North, at 9 p.m., towards mid-September. It appears instead at the zenith for a long period between mid January and mid February. Towards the end of June it begins to set in the north-eastern horizon.

Its northernmost part, a little to the north of Capella, is circumpolar and can be seen all year round, but it has no particularly bright stars.

Audio Video The constellation of Charioteer (Auriga - Aur)
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