Capella is Alpha Aurigae (α Aur), HD 34029 and HIP 24608, permanent object 27. The stored visual magnitude is about 0.08. A detailed orbital study describes the principal pair as G8 III + G0 III in a 104-day orbit. The system also has a distant common-proper-motion companion that is itself a pair of red dwarfs, making the wider system hierarchical and quadruple. Source: Torres et al. (2015), https://arxiv.org/abs/1505.07461.
For the close bright pair, Torres and collaborators measured masses of 2.5687 ± 0.0074 and 2.4828 ± 0.0067 solar masses. Their radii are about 11.98 and 8.83 times the Sun's, and their effective temperatures about 4,970 and 5,730 kelvin. Both are giants, yet the slightly more massive, cooler primary is near the end of core helium burning while the hotter secondary is crossing the Hertzsprung gap rapidly. Nearly equal starting mass has not produced identical present appearance because stellar evolution accelerates and changes direction in this phase.
The measurements also expose uncertainty rather than eliminating it. Three model families matched the revised masses, composition and broad evolutionary state well, but standard tidal calculations did not reproduce all the observed spin and alignment properties without greatly increasing the assumed dissipation efficiency. That mismatch is scientifically useful: Capella is a benchmark precisely because masses, radii, chemistry and orbit can confront stellar-evolution and tidal theories together.
The pair does not eclipse from Earth's line of sight, so its properties cannot be read from periodic disappearances. Astronomers instead combine changing spectral-line velocities with astrometric and interferometric orbital measurements. The quoted masses and radii are therefore a synthesis of complementary observations, not values inferred merely from Capella's brightness.
Capella means “little she-goat” in Latin, and the star traditionally marks the goat carried by Auriga, the Charioteer. The IAU-approved proper name belongs to the combined naked-eye light, while Alpha Aurigae is its Bayer designation. Official name guidance: https://www.iau.org/public/themes/naming_stars/. Its status as Alpha fits its brilliance, but the letter itself is still a historical label rather than a physical category.
The stored position is approximately right ascension 5h 17m and declination +46° 00′. At latitude 45° N it passes within about one degree of the zenith at upper culmination and just clears the geometric northern horizon at lower culmination. It is circumpolar north of roughly latitude 44° N. At 35° S it reaches only about 9° altitude. These original calculations ignore refraction, terrain and buildings; the southern case is especially vulnerable to extinction near the horizon.
Capella is the brightest point in Auriga's accepted figure. Follow the polygon southward toward the other bright Charioteer stars, and verify Capella as its northern vertex. It is also the northern vertex of the repository's accepted Winter Hexagon, between Aldebaran and Pollux. These relationships are strong naked-eye guidance, but the rendered finder and reader link still need publication-stage inspection.
Capella is effortless to see without optical aid, yet the close giants are not cleanly separated in an ordinary small telescope; the eye receives their combined light. A modest telescope may show unrelated field stars, while specialized spectroscopy and interferometry reveal the orbit. Record colour cautiously because contrast, altitude and eye adaptation affect the warm impression. Weekly darkness and timing belong in the almanac, not the permanent story.
