Auriga … and You Charioteer or Goatherd?
[Sidney Hall (1788-1831), Restoration by Adam Cuerden
Our constellation for February rides high in the sky over Orion and Aldebaran in Taurus. As you see in the sky chart, a line drawn from Orion’s belt up between his shoulders leads you to the large pentagon and the bright twinkler Capella, the charioteer’s alpha star and western shoulder. That line crosses the lengthy horns of Taurus, one of which extends from the Hyades “V” to El Nath, the beta star, and a star seemingly shared by the two constellations.
A little mythology helps with understanding the Auriga (aw'-ri-gah) story. He is identified with the Greek god Hephaestus (Roman, Vulcan) or his son, both of whom were lame. This god is credited with the invention of the chariot – for obvious purposes. The story makes me think of Porgy on his little dolly in the Gershwin musical. But there is more. Some legends blend the chariot story with the legend of the goatherd. The bright Capella is sometimes depicted as having a goat draped over it, and you’ll notice three stars just to the south which the story tells us are the kids carried on the goatherd’s arm. Capella is northerly enough so that it is visible for some portion of every night of the year. Its flashes are attributed by some to be from our atmospheric interventions, and by others as stemming from the fact that it is a system of 3 or four stars. Capella is always twinkling away when I see it.
Auriga (south-central region)
[Credit Roberto Mura, Creative Commons Attribution-Share Alike 3.0 Unported license]
The chart above shows the southerly half and three corners of the pentagon – Bogardus, El Nath, and Hassaleh. Philip Harrington, author of books for binocular observers, reports his joy upon seeing Auriga each year. There are many clusters of star to views in this region, for example the rope ladder draped from star #19; however, three principle performers stand out. The open clusters M37, M36, and M38 (small yellow circles) can be seen as smudgy objects even with unaided eyes. Binoculars may reveal some individual characteristics, such as size, shape, numerosity.
Auriga also boasts many variable stars of the type known as eclipsing binaries. These objects contain two or more stars in mutual gravitational tow. The brightness makes a measurable change if one star obscures another in our line of sight. Those changes can be displayed in a graph known as a light curve, and we can learn much about the nature of the orbits and of the stars themselves.
Some light curves show rapid drops and rises, and others, more gradual changes. These give clues about atmospheric conditions on the eclipsing star. Some curves show two distinct and constant light levels, indicating total rather than partial eclipses. Some curves are spiky indicating turbulent outbursts. Some curves are very irregular, and they leave more questions than answers.
One star, RT Auriga presents a light curve identifying it as a cepheid variable, a type of great historical significance. Rather than a star system, these are single stars that expand and contract in very regular cycles of a few days. The timing of those cycles correlates directly with the heat of the star. So the cycle predicts what “color” the star is, but that color can be shifted toward red for more distant stars. In 1923 Edwin Hubble found these cepheid stars in the Andromeda “nebula,” and their color indicated they were millions of light years away, far from any part of the Milky Way. The universe grew enormously in our understanding, and Andromeda was re-classified as the second known galaxy.
... and You
1. Cornucopia. Capella is sometimes called the Cornucopia star. Its incessant twinkling suggests to me that many goodies are pouring from it. What is the connection with Auriga, the goatherd?
2. Epsilon Auriga. Just one of the kids? Epsilon Auriga, just south of Capella, the goatherd’s shoulder, is one of the strangest objects in the sky. It’s light curve indicates an eclipsing binary, but just what type of huge, mysterious object does the eclipsing is unclear. In the 1970s Burnham reported on three theories. Find out what’s happened since. Have a look at the light curve. Read about the scientists who tracked this strange kid down.
3. Light curves for cepheid variable stars and other types. Without instruments, our own eyes can gauge changes in luminosity by comparing two nearby stars – one, not a variable. Find out about various variable types. Learn how cepheid periods – cycles of brighter and dimmer – are used to determine distance.
4. Using binoculars, observe and then sketch the major stars and their patterns in the three main clusters M38, M36, and M37. Find the distances to these clusters. Look for color variations in M37.
Below are my findings.
The clusters all looked like gray fuzzy balls. They appeared to be different sizes. I noticed that if I used averted vision, looking slightly to one side or the other, some stars would spark through the clouds. In M37 I did detect a formation of brighter stars to the left (east), similar to the Hyades V-shape.
With binoculars, you might not have realized the degree of detail in your sketches of the main Auriga clusters as was achieved telescopically in the gallery, but celebrate any details you did achieve. The clusters' Messier catalog numbers along with the object distances from us are given below the images [and credits below]. Perspective shocker: from these distances, our Sun and its neighboring stars would have the appearance of a cluster like one of these.
Check out the Auriga Gallery.