Capella is Alpha Aurigae, apparent magnitude 0.08, at 43 light years, and it is the sixth-brightest star in the sky and the closest first-magnitude star to the north celestial pole, circumpolar from most of Europe, so it never sets.
What appears as one star is four. Capella A and B are two yellow giants of spectral types around G1 III and K0 III, both considerably more massive and far more luminous than the Sun, orbiting each other in about 104 days at a separation of roughly the Earth-Sun distance. They cannot be separated visually and were identified spectroscopically; Capella was among the first spectroscopic binaries discovered. A distant pair of faint red dwarfs, Capella H and L, completes the system.
The two giants are of nearly equal mass and are at different evolutionary stages, which makes the system unusually valuable for testing models of stellar evolution: two stars of known and almost identical mass, formed together, caught at different points. The more evolved of the pair is in a rapid transitional phase.
The Latin Capella means little she-goat, and the star is the goat carried on the shoulder of Auriga, the Charioteer, a constellation figure that makes very little narrative sense and appears to be a conflation of separate traditions. The associated Haedi, the Kids, are the nearby fainter stars, and their rising and setting were weather markers in classical agricultural writing, associated with storms.
The incoherence of the figure is worth dwelling on, because it is common and usually smoothed over. A charioteer has no obvious reason to carry a goat and her kids, and none to be drawn without a chariot, which Auriga is. The likeliest explanation is that two or more older figures were merged when the Greek constellation set was assembled from Mesopotamian material, and the seams were never tidied.
Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Almagest (Mathematike Syntaxis)Claudius Ptolemy