Capella

Capella is the sixth brightest star in the night sky at magnitude 0.08, located in the constellation Auriga about 43 light-years from Earth. It is actually a spectroscopic binary system consisting of two yellow giant stars: Capella Aa (spectral type G8III, about 79 solar luminosities) and Capella Ab (G1III, about 78 solar luminosities), orbiting each other every 104 days at a separation of about 0.74 AU. A distant pair of red dwarfs (Capella H and L) also belongs to the system.

Capella is easily recognized as the brilliant yellowish star high in the northern sky during winter evenings. It forms a distinctive pentagon shape with the other bright stars of Auriga. The binary nature of Capella cannot be resolved visually — the two giant stars orbit too closely (0.05 arcseconds) — but their combined light makes a striking golden beacon. The nearby open clusters M36, M37, and M38 in Auriga make excellent binocular targets in the same region. Best observed from October through April. Capella is circumpolar from latitudes north of about 44°N.

The name Capella means 'little she-goat' in Latin, associated with the mythological goat Amalthea that suckled the infant Zeus. The Romans called it 'Capra.' It was listed in most ancient star catalogs, including Ptolemy's Almagest. The binary nature of Capella was discovered spectroscopically in 1899, and interferometric observations have since directly measured the orbit of the two giant components.