Capella is the sixth brightest star in the night sky,
a quadruple star system of two binary-star pairs, the four
termed Capella Aa, Capella Ab, Capella H, and Capella L.
The former two are both giant stars, about as distant from
each other as the Sun and Venus, but without a telescope
they appear as a single star. The latter two are M dwarfs
and invisible without a telescope.
Capella is a strong X-ray source, the X-rays thought to stem
from stellar activity affecting Capella Aa's corona.
Characteristics of Capella A: