The Heavenly Golden Goat

While you won’t find the chariot in this star’s
constellation, you can’t miss Capella

Between 9 and 10 o’clock this week, look directly overhead to the golden giant Alpha Aur, or Capella. The main star in the constellation Auriga, Capella is the sixth brightest star and the most northerly first-magnitude star.

It is also one of only a few yellow stars, our own sun being another, all of which are around the same age, burning roughly the same mix of fuel at around the same temperature. The similarities end there, however, as Capella is in truth four stars: two yellow giants and two red dwarfs.

The majority of the light we see comes from the two yellow giants, Capella Aa and Capella Ab, which revolve around one another every 104 days in an orbit tighter than Earth’s orbit around the sun. Capella Aa is three times more massive than our sun, while Capella Ab is more than two and a half times the sun’s mass. The two shine with a combined luminosity 130 times greater than the sun, so that were someone in the stars’ system looking across the 42 light years toward us, our sun would be lost among the myriad stars of the Milky Way.

Capella, from the Latin caper, for goat, is known as the Shepherd’s Star, but its parent constellation has been seen through the ages as a chariot. In ancient China, Auriga represented the five chariots of the five celestial emperors. The Babylonians, as well, saw a chariot in this pattern of stars. Yet today Auriga, Latin for charioteer, appears bereft of both chariot and horse, holding only a pair of reins in one hand. Instead, he sits with the she-goat Capella nestled in the crook of his arm while two kids rest in his lap.